8-bit string internally tests

Lexing/Parsing is done on byte rather than js strings

17 files changed, 201 insertions, 199 deletions

diff --git a/src/lapi.js b/src/lapi.js
index 6e1471d..e7fbf4f 100644
--- a/src/lapi.js
+++ b/src/lapi.js
@@ -678,7 +678,7 @@ const lua_compare_ = function(L, o1, o2, op) {
 };
 
 const lua_stringtonumber = function(L, s) {
-    let number = parseFloat(s);
+    let number = parseFloat(lobject.jsstring(s));
     L.stack[L.top++] = new TValue(number % 1 !== 0 ? CT.LUA_TNUMFLT : CT.LUA_TNUMINT, number);
     assert(L.top <= L.ci.top, "stack overflow");
     return s.length;
@@ -980,6 +980,8 @@ module.exports.lua_toboolean         = lua_toboolean;
 module.exports.lua_todataview        = lua_todataview;
 module.exports.lua_tointeger         = lua_tointeger;
 module.exports.lua_tointegerx        = lua_tointegerx;
+module.exports.lua_tojsstring        = lua_tojsstring;
+module.exports.lua_toljsstring       = lua_toljsstring;
 module.exports.lua_tolstring         = lua_tolstring;
 module.exports.lua_tonumber          = lua_tonumber;
 module.exports.lua_topointer         = lua_topointer;
diff --git a/src/lauxlib.js b/src/lauxlib.js
index f60bd8c..9813095 100644
--- a/src/lauxlib.js
+++ b/src/lauxlib.js
@@ -55,7 +55,7 @@ const findfield = function(L, objidx, level) {
 const pushglobalfuncname = function(L, ar) {
     let top = lapi.lua_gettop(L);
     ldebug.lua_getinfo(L, 'f', ar);  /* push function */
-    lapi.lua_getfield(L, lua.LUA_REGISTRYINDEX, LUA_LOADED_TABLE);
+    lapi.lua_getfield(L, lua.LUA_REGISTRYINDEX, lua.to_luastring(LUA_LOADED_TABLE));
     if (findfield(L, top + 1, 2)) {
         let name = lapi.lua_tostring(L, -1);
         if (name.jsstring().startsWith("_G.")) {
@@ -333,7 +333,7 @@ const luaL_tolstring = function(L, idx) {
 ** Leaves resulting module on the top.
 */
 const luaL_requiref = function(L, modname, openf, glb) {
-    luaL_getsubtable(L, lua.LUA_REGISTRYINDEX, LUA_LOADED_TABLE);
+    luaL_getsubtable(L, lua.LUA_REGISTRYINDEX, lua.to_luastring(LUA_LOADED_TABLE));
     lapi.lua_getfield(L, -1, modname); /* LOADED[modname] */
     if (!lapi.lua_toboolean(L, -1)) {  /* package not already loaded? */
         lapi.lua_pop(L, 1);  /* remove field */
@@ -441,7 +441,7 @@ if (typeof require === "function") {
                 lf.pos += bytes;
             }
             if (bytes > 0)
-                return lf.binary ? toDataView(lf.buff) : lf.buff;
+                return lf.binary ? toDataView(lf.buff) : lf.buff.slice(0, bytes);
             else return null;
         };
 
@@ -502,15 +502,16 @@ if (typeof require === "function") {
         };
 
         const luaL_loadfilex = function(L, filename, mode) {
+            let jsfilename = lobject.jsstring(filename);
             let lf = new LoadF();
             let fnameindex = lapi.lua_gettop(L) + 1;  /* index of filename on the stack */
             if (filename === null) {
                 lapi.lua_pushliteral(L, "=stdin");
                 lf.f = process.stdin.fd;
             } else {
-                lapi.lua_pushliteral(L, `@${filename}`);
+                lapi.lua_pushliteral(L, `@${jsfilename}`);
                 try {
-                    lf.f = fs.openSync(filename, "r");
+                    lf.f = fs.openSync(jsfilename, "r");
                 } catch (e) {
                     return errfile(L, lua.to_luastring("open"), fnameindex, e);
                 }
diff --git a/src/lbaselib.js b/src/lbaselib.js
index 8420672..4d0fb9c 100644
--- a/src/lbaselib.js
+++ b/src/lbaselib.js
@@ -11,7 +11,7 @@ const TS      = lua.thread_status;
 
 const luaB_print = function(L) {
     let n = lapi.lua_gettop(L); /* number of arguments */
-    let str = "";
+    let str = [];
 
     lapi.lua_getglobal(L, lua.to_luastring("tostring"));
     for (let i = 1; i <= n; i++) {
@@ -201,7 +201,7 @@ const luaB_assert = function(L) {
 
 const luaB_select = function(L) {
     let n = lapi.lua_gettop(L);
-    if (lapi.lua_type(L, 1) === CT.LUA_TSTRING && lapi.lua_tostring(L, 1) === "#") {
+    if (lapi.lua_type(L, 1) === CT.LUA_TSTRING && lapi.lua_tostring(L, 1)[0] === "#".charCodeAt(0)) {
         lapi.lua_pushinteger(L, n - 1);
         return 1;
     } else {
diff --git a/src/lcode.js b/src/lcode.js
index 8b4a57c..752eedf 100644
--- a/src/lcode.js
+++ b/src/lcode.js
@@ -1231,7 +1231,7 @@ const luaK_setlist = function(fs, base, nelems, tostore) {
         codeextraarg(fs, c);
     }
     else
-        llex.luaX_syntaxerror(fs.ls, "constructor too long");
+        llex.luaX_syntaxerror(fs.ls, lua.to_luastring("constructor too long"));
     fs.freereg = base + 1;  /* free registers with list values */
 };
 
diff --git a/src/ldebug.js b/src/ldebug.js
index 507e764..0fba4cb 100644
--- a/src/ldebug.js
+++ b/src/ldebug.js
@@ -431,7 +431,7 @@ const varinfo = function(L, o) {
             kind = getobjname(ci.func.p, ci.pcOff, stkid - ci.u.l.base);
     }
 
-    return lua.to_luastring(kind ? ` (${lobject.jsstring(kind.funcname)} '${lobject.jsstring(kind.name)}')` : ``);
+    return lua.to_luastring(kind ? ` (${lobject.jsstring(kind.funcname)} '${kind.name.jsstring()}')` : ``);
 };
 
 const luaG_typeerror = function(L, o, op) {
@@ -457,7 +457,7 @@ const luaG_opinterror = function(L, p1, p2, msg) {
 const luaG_ordererror = function(L, p1, p2) {
     let t1 = ltm.luaT_objtypename(L, p1);
     let t2 = ltm.luaT_objtypename(L, p2);
-    if (t1 === t2)
+    if (t1.join() === t2.join())
         luaG_runerror(L, lua.to_luastring(`attempt to compare two ${lobject.jsstring(t1)} values`));
     else
         luaG_runerror(L, lua.to_luastring(`attempt to compare ${lobject.jsstring(t1)} with ${lobject.jsstring(t2)}`));
diff --git a/src/ldo.js b/src/ldo.js
index 54d1ac0..6a74cad 100644
--- a/src/ldo.js
+++ b/src/ldo.js
@@ -519,8 +519,8 @@ class SParser {
 }
 
 const checkmode = function(L, mode, x) {
-    if (mode && mode.indexOf(x.charCodeAt(0)) === -1) {
-        lapi.lua_pushstring(L, lua.to_luastring(`attempt to load a ${lobject.jsstring(x)} chunk (mode is '${mode}')`));
+    if (mode && mode.indexOf(x[0]) === -1) {
+        lapi.lua_pushstring(L, lua.to_luastring(`attempt to load a ${lobject.jsstring(x)} chunk (mode is '${lobject.jsstring(mode)}')`));
         luaD_throw(L, TS.LUA_ERRSYNTAX);
     }
 };
@@ -528,11 +528,11 @@ const checkmode = function(L, mode, x) {
 const f_parser = function(L, p) {
     let cl;
     let c = p.z.getc();  /* read first character */
-    if (String.fromCharCode(c) === lua.LUA_SIGNATURE.charAt(0)) {
-        checkmode(L, p.mode, "binary");
+    if (c === lua.LUA_SIGNATURE.charCodeAt(0)) {
+        checkmode(L, p.mode, lua.to_luastring("binary"));
         cl = new BytecodeParser(L, p.z.buffer).luaU_undump();
     } else {
-        checkmode(L, p.mode, "text");
+        checkmode(L, p.mode, lua.to_luastring("text"));
         cl = lparser.luaY_parser(L, p.z, p.buff, p.dyd, p.name, c);
     }
 
diff --git a/src/linit.js b/src/linit.js
index 4d50f8b..3e9b1af 100644
--- a/src/linit.js
+++ b/src/linit.js
@@ -2,6 +2,7 @@
 
 const assert = require('assert');
 
+const lua      = require('./lua.js');
 const lapi     = require('./lapi.js');
 const lauxlib  = require('./lauxlib.js');
 const lbaselib = require('./lbaselib.js');
@@ -24,9 +25,9 @@ const loadedlibs = {
 const luaL_openlibs = function(L) {
     /* "require" functions from 'loadedlibs' and set results to global table */
     for (let lib in loadedlibs) {
-        lauxlib.luaL_requiref(L, lib, loadedlibs[lib], 1);
+        lauxlib.luaL_requiref(L, lua.to_luastring(lib), loadedlibs[lib], 1);
         lapi.lua_pop(L, 1); /* remove lib */
     }
 };
 
-module.exports.luaL_openlibs = luaL_openlibs;
\ No newline at end of file
+module.exports.luaL_openlibs = luaL_openlibs;
diff --git a/src/llex.js b/src/llex.js
index 9b81cd7..e043c17 100644
--- a/src/llex.js
+++ b/src/llex.js
@@ -15,6 +15,12 @@ const TS       = lua.thread_status;
 
 const FIRST_RESERVED = 257;
 
+// To avoid charCodeAt everywhere
+const char = [];
+for (let i = 0; i < 127; i++)
+    char[String.fromCharCode(i)] = i;
+module.exports.char = char;
+
 const RESERVED = {
     /* terminal symbols denoted by reserved words */
     TK_AND:      FIRST_RESERVED,
@@ -157,7 +163,7 @@ const save = function(ls, c) {
 
 const luaX_token2str = function(ls, token) {
     if (typeof token === "string" || token < FIRST_RESERVED) {  /* single-byte symbols? */
-        return lua.to_luastring(`'${typeof token === "string" ? token : lobject.jsstring(token)}'`);
+        return lua.to_luastring(`'${typeof token === "string" ? token : lobject.jsstring([token])}'`);
     } else {
         let s = luaX_tokens[token - FIRST_RESERVED];
         if (token < R.TK_EOS)  /* fixed format (symbols and reserved words)? */
@@ -168,7 +174,7 @@ const luaX_token2str = function(ls, token) {
 };
 
 const currIsNewline = function(ls) {
-    return ls.current === '\n'.charCodeAt(0) || ls.current === '\r'.charCodeAt(0);
+    return ls.current === char['\n'] || ls.current === char['\r'];
 };
 
 const next = function(ls) {
@@ -235,7 +241,7 @@ const check_next1 = function(ls, c) {
 ** saves it
 */
 const check_next2 = function(ls, set) {
-    if (ls.current === set.charAt(0).charCodeAt(0) || ls.current === set.charAt(1).charCodeAt(0)) {
+    if (ls.current === set[0].charCodeAt(0) || ls.current === set[1].charCodeAt(0)) {
         save_and_next(ls);
         return true;
     }
@@ -248,7 +254,7 @@ const read_numeral = function(ls, seminfo) {
     let first = ls.current;
     assert(ljstype.lisdigit(ls.current));
     save_and_next(ls);
-    if (first === '0' && check_next2(ls, "xX"))  /* hexadecimal? */
+    if (first === char['0'] && check_next2(ls, "xX"))  /* hexadecimal? */
         expo = "Pp";
 
     for (;;) {
@@ -256,7 +262,7 @@ const read_numeral = function(ls, seminfo) {
             check_next2(ls, "-+");  /* optional exponent sign */
         if (ljstype.lisxdigit(ls.current))
             save_and_next(ls);
-        else if (ls.current === '.')
+        else if (ls.current === char['.'])
             save_and_next(ls);
         else break;
     }
@@ -295,7 +301,6 @@ const lexerror = function(ls, msg, token) {
 };
 
 const luaX_syntaxerror = function(ls, msg) {
-    msg = msg instanceof TValue ? msg.value : lua.to_luastring(msg);
     lexerror(ls, msg, ls.t.token);
 };
 
@@ -307,9 +312,9 @@ const luaX_syntaxerror = function(ls, msg) {
 const skip_sep = function(ls) {
     let count = 0;
     let s = ls.current;
-    assert(s === '['.charCodeAt(0) || s === ']'.charCodeAt(0));
+    assert(s === char['['] || s === char[']']);
     save_and_next(ls);
-    while (ls.current === '='.charCodeAt(0)) {
+    while (ls.current === char['=']) {
         save_and_next(ls);
         count++;
     }
@@ -332,15 +337,15 @@ const read_long_string = function(ls, seminfo, sep) {
                 lexerror(ls, lua.to_luastring(msg), R.TK_EOS);
                 break;
             }
-            case ']'.charCodeAt(0): {
+            case char[']']: {
                 if (skip_sep(ls) === sep) {
                     save_and_next(ls);  /* skip 2nd ']' */
                     skip = true;
                 }
                 break;
             }
-            case '\n'.charCodeAt(0): case '\r'.charCodeAt(0): {
-                save(ls, '\n'.charCodeAt(0));
+            case char['\n']: case char['\r']: {
+                save(ls, char['\n']);
                 inclinenumber(ls);
                 if (!seminfo) {
                     ls.buff.n = 0;
@@ -386,7 +391,7 @@ const readhexaesc = function(ls) {
 const readutf8desc = function(ls) {
     let i = 4;  /* chars to be removed: '\', 'u', '{', and first digit */
     save_and_next(ls);  /* skip 'u' */
-    esccheck(ls, ls.current === '{'.charCodeAt(0), lua.to_luastring("missing '{'"));
+    esccheck(ls, ls.current === char['{'], lua.to_luastring("missing '{'"));
     let r = gethexa(ls);  /* must have at least one digit */
 
     save_and_next(ls);
@@ -396,7 +401,7 @@ const readutf8desc = function(ls) {
         esccheck(ls, r <= 0x10FFFF, lua.to_luastring("UTF-8 value too large"));
         save_and_next(ls);
     }
-    esccheck(ls, ls.current === '}'.charCodeAt(0), lua.to_luastring("missing '}'"));
+    esccheck(ls, ls.current === char['}'], lua.to_luastring("missing '}'"));
     next(ls);  /* skip '}' */
     ls.buff.n -= i;  /* remove saved chars from buffer */
     return r;
@@ -429,30 +434,30 @@ const read_string = function(ls, del, seminfo) {
             case -1:
                 lexerror(ls, lua.to_luastring("unfinished string"), R.TK_EOS);
                 break;
-            case '\n'.charCodeAt(0):
-            case '\r'.charCodeAt(0):
+            case char['\n']:
+            case char['\r']:
                 lexerror(ls, lua.to_luastring("unfinished string"), R.TK_STRING);
                 break;
-            case '\\'.charCodeAt(0): {  /* escape sequences */
+            case char['\\']: {  /* escape sequences */
                 save_and_next(ls);  /* keep '\\' for error messages */
                 let will;
                 let c;
                 switch(ls.current) {
-                    case 'a': c = '\a'.charCodeAt(0); will = 'read_save'; break;
-                    case 'b': c = '\b'.charCodeAt(0); will = 'read_save'; break;
-                    case 'f': c = '\f'.charCodeAt(0); will = 'read_save'; break;
-                    case 'n': c = '\n'.charCodeAt(0); will = 'read_save'; break;
-                    case 'r': c = '\r'.charCodeAt(0); will = 'read_save'; break;
-                    case 't': c = '\t'.charCodeAt(0); will = 'read_save'; break;
-                    case 'v': c = '\v'.charCodeAt(0); will = 'read_save'; break;
-                    case 'x': c = readhexaesc(ls); will = 'read_save'; break;
-                    case 'u': utf8esc(ls); will = 'no_save'; break;
-                    case '\n'.charCodeAt(0): case '\r'.charCodeAt(0):
-                        inclinenumber(ls); c = '\n'; will = 'only_save'; break;
-                    case '\\'.charCodeAt(0): case '\"'.charCodeAt(0): case '\''.charCodeAt(0):
+                    case char['a']: c = char['\a']; will = 'read_save'; break;
+                    case char['b']: c = char['\b']; will = 'read_save'; break;
+                    case char['f']: c = char['\f']; will = 'read_save'; break;
+                    case char['n']: c = char['\n']; will = 'read_save'; break;
+                    case char['r']: c = char['\r']; will = 'read_save'; break;
+                    case char['t']: c = char['\t']; will = 'read_save'; break;
+                    case char['v']: c = char['\v']; will = 'read_save'; break;
+                    case char['x']: c = readhexaesc(ls); will = 'read_save'; break;
+                    case char['u']: utf8esc(ls); will = 'no_save'; break;
+                    case char['\n']: case char['\r']:
+                        inclinenumber(ls); c = char['\n']; will = 'only_save'; break;
+                    case char['\\']: case char['\"']: case char['\'']:
                         c = ls.current; will = 'read_save'; break;
                     case -1: will = 'no_save'; break;  /* will raise an error next loop */
-                    case 'z': {  /* zap following span of spaces */
+                    case char['z']: {  /* zap following span of spaces */
                         ls.buff.n -= 1;  /* remove '\\' */
                         next(ls);  /* skip the 'z' */
                         while (ljstype.lisspace(ls.current)) {
@@ -500,20 +505,20 @@ const llex = function(ls, seminfo) {
 
     for (;;) {
         switch (ls.current) {
-            case '\n'.charCodeAt(0): case '\r'.charCodeAt(0): {  /* line breaks */
+            case char['\n']: case char['\r']: {  /* line breaks */
                 inclinenumber(ls);
                 break;
             }
-            case ' '.charCodeAt(0): case '\f'.charCodeAt(0): case '\t'.charCodeAt(0): case '\v'.charCodeAt(0): {  /* spaces */
+            case char[' ']: case char['\f']: case char['\t']: case char['\v']: {  /* spaces */
                 next(ls);
                 break;
             }
-            case '-'.charCodeAt(0): {  /* '-' or '--' (comment) */
+            case char['-']: {  /* '-' or '--' (comment) */
                 next(ls);
-                if (ls.current !== '-'.charCodeAt(0)) return '-';
+                if (ls.current !== char['-']) return char['-'];
                 /* else is a comment */
                 next(ls);
-                if (ls.current === '['.charCodeAt(0)) {  /* long comment? */
+                if (ls.current === char['[']) {  /* long comment? */
                     let sep = skip_sep(ls);
                     ls.buff.n = 0;  /* 'skip_sep' may dirty the buffer */
                     ls.buff.buffer = [];
@@ -530,63 +535,63 @@ const llex = function(ls, seminfo) {
                     next(ls);  /* skip until end of line (or end of file) */
                 break;
             }
-            case '['.charCodeAt(0): {  /* long string or simply '[' */
+            case char['[']: {  /* long string or simply '[' */
                 let sep = skip_sep(ls);
                 if (sep >= 0) {
                     read_long_string(ls, seminfo, sep);
                     return R.TK_STRING;
                 } else if (sep !== -1)  /* '[=...' missing second bracket */
                     lexerror(ls, lua.to_luastring("invalid long string delimiter"), R.TK_STRING);
-                return '[';
+                return char['['];
             }
-            case '='.charCodeAt(0): {
+            case char['=']: {
                 next(ls);
                 if (check_next1(ls, '=')) return R.TK_EQ;
-                else return '=';
+                else return char['='];
             }
-            case '<'.charCodeAt(0): {
+            case char['<']: {
                 next(ls);
                 if (check_next1(ls, '=')) return R.TK_LE;
                 else if (check_next1(ls, '<')) return R.TK_SHL;
-                else return '<';
+                else return char['<'];
             }
-            case '>'.charCodeAt(0): {
+            case char['>']: {
                 next(ls);
                 if (check_next1(ls, '=')) return R.TK_GE;
                 else if (check_next1(ls, '>')) return R.TK_SHR;
-                else return '>';
+                else return char['>'];
             }
-            case '/'.charCodeAt(0): {
+            case char['/']: {
                 next(ls);
                 if (check_next1(ls, '/')) return R.TK_IDIV;
-                else return '/';
+                else return char['/'];
             }
-            case '~'.charCodeAt(0): {
+            case char['~']: {
                 next(ls);
                 if (check_next1(ls, '=')) return R.TK_NE;
-                else return '~';
+                else return char['~'];
             }
-            case ':'.charCodeAt(0): {
+            case char[':']: {
                 next(ls);
                 if (check_next1(ls, ':')) return R.TK_DBCOLON;
-                else return ':';
+                else return char[':'];
             }
-            case '"'.charCodeAt(0): case '\''.charCodeAt(0): {  /* short literal strings */
+            case char['"']: case char['\'']: {  /* short literal strings */
                 read_string(ls, ls.current, seminfo);
                 return R.TK_STRING;
             }
-            case '.'.charCodeAt(0): {  /* '.', '..', '...', or number */
+            case char['.']: {  /* '.', '..', '...', or number */
                 save_and_next(ls);
                 if (check_next1(ls, '.')) {
                     if (check_next1(ls, '.'))
                         return R.TK_DOTS;   /* '...' */
                     else return R.TK_CONCAT;   /* '..' */
                 }
-                else if (!ljstype.lisdigit(ls.current)) return '.';
+                else if (!ljstype.lisdigit(ls.current)) return char['.'];
                 else return read_numeral(ls, seminfo);
             }
-            case '0': case '1': case '2': case '3': case '4':
-            case '5': case '6': case '7': case '8': case '9': {
+            case char['0']: case char['1']: case char['2']: case char['3']: case char['4']:
+            case char['5']: case char['6']: case char['7']: case char['8']: case char['9']: {
                 return read_numeral(ls, seminfo);
             }
             case -1: {
@@ -598,7 +603,7 @@ const llex = function(ls, seminfo) {
                         save_and_next(ls);
                     } while (ljstype.lislalnum(ls.current));
 
-                    let ts = new TValue(CT.LUA_TLNGSTR, lua.to_luastring(ls.buff.buffer.join('')));
+                    let ts = new TValue(CT.LUA_TLNGSTR, ls.buff.buffer);
                     seminfo.ts = ts;
                     let kidx = luaX_tokens.slice(0, 22).indexOf(ts.jsstring());
                     if (kidx >= 0)  /* reserved word? */
diff --git a/src/lobject.js b/src/lobject.js
index 812ac6a..e958975 100644
--- a/src/lobject.js
+++ b/src/lobject.js
@@ -132,6 +132,8 @@ const luaO_nilobject = new TValue(CT.LUA_TNIL, null);
 module.exports.luaO_nilobject = luaO_nilobject;
 
 const jsstring = function(value, from, to) {
+    assert(Array.isArray(value), "jsstring expect a array of bytes");
+
     let u0, u1, u2, u3, u4, u5;
     let idx = 0;
     value = value.slice(from ? from : 0, to);
@@ -194,6 +196,8 @@ class Table extends TValue {
             }
         } else if (typeof key === "string") { // To avoid
             key = lua.to_luastring(key).map(e => `${e}|`).join('');
+        } else if (Array.isArray(key)) {
+            key = key.map(e => `${e}|`).join('');
         }
 
         return key;
@@ -293,7 +297,7 @@ const luaO_chunkid = function(source, bufflen) {
         else {  /* truncate it */
             out = out.concat(source.slice(1, bufflen));
         }
-    } else if (source.charAt(0) === '@') {  /* file name */
+    } else if (source[0] === '@'.charCodeAt(0)) {  /* file name */
         if (l <= bufflen)  /* small enough? */
             out = source.slice(1);
         else {  /* add '...' before rest of name */
diff --git a/src/lparser.js b/src/lparser.js
index 01b9a08..249d51f 100644
--- a/src/lparser.js
+++ b/src/lparser.js
@@ -18,6 +18,8 @@ const Table    = lobject.Table;
 const UnOpr    = lcode.UnOpr;
 const UpVal    = lfunc.UpVal;
 
+const char     = llex.char;
+
 const MAXVARS = 200;
 
 const hasmultret = function(k) {
@@ -248,7 +250,7 @@ const new_localvar = function(ls, name) {
 };
 
 const new_localvarliteral = function(ls, name) {
-    new_localvar(ls, new TValue(lua.CT.LUA_TLNGSTR, lua.to_luastring(name)));
+    new_localvar(ls, new TValue(lua.CT.LUA_TLNGSTR, name));
 };
 
 const getlocvar = function(fs, i) {
@@ -273,7 +275,7 @@ const removevars = function(fs, tolevel) {
 const searchupvalue = function(fs, name) {
     let up = fs.f.upvalues;
     for (let i = 0; i < fs.nups; i++) {
-        if (up[i].name.join() === name.join())
+        if (up[i].name.value.join() === name.value.join())
             return i;
     }
     return -1;  /* not found */
@@ -291,7 +293,7 @@ const newupvalue = function(fs, name, v) {
 
 const searchvar = function(fs, n) {
     for (let i = fs.nactvar - 1; i >= 0; i--) {
-        if (n.join() === getlocvar(fs, i).varname.join())
+        if (n.value.join() === getlocvar(fs, i).varname.value.join())
             return i;
     }
 
@@ -611,7 +613,7 @@ const yindex = function(ls, v) {
     llex.luaX_next(ls);  /* skip the '[' */
     expr(ls, v);
     lcode.luaK_exp2val(ls.fs, v);
-    checknext(ls, ']');
+    checknext(ls, char[']']);
 };
 
 /*
@@ -643,7 +645,7 @@ const recfield = function(ls, cc) {
     } else  /* ls->t.token === '[' */
         yindex(ls, key);
     cc.nh++;
-    checknext(ls, '=');
+    checknext(ls, char['=']);
     let rkkey = lcode.luaK_exp2RK(fs, key);
     expr(ls, val);
     lcode.luaK_codeABC(fs, OpCodesI.OP_SETTABLE, cc.t.u.info, rkkey, lcode.luaK_exp2RK(fs, val));
@@ -685,13 +687,13 @@ const field = function(ls, cc) {
     /* field -> listfield | recfield */
     switch (ls.t.token) {
         case R.TK_NAME: {  /* may be 'listfield' or 'recfield' */
-            if (llex.luaX_lookahead(ls) !== '=')  /* expression? */
+            if (llex.luaX_lookahead(ls) !== char['='])  /* expression? */
                 listfield(ls, cc);
             else
                 recfield(ls, cc);
             break;
         }
-        case '[': {
+        case char['[']: {
             recfield(ls, cc);
             break;
         }
@@ -714,14 +716,14 @@ const constructor = function(ls, t) {
     init_exp(t, expkind.VRELOCABLE, pc);
     init_exp(cc.v, expkind.VVOID, 0);  /* no value (yet) */
     lcode.luaK_exp2nextreg(ls.fs, t);  /* fix it at stack top */
-    checknext(ls, '{');
+    checknext(ls, char['{']);
     do {
         assert(cc.v.k === expkind.VVOID || cc.tostore > 0);
-        if (ls.t.token === '}') break;
+        if (ls.t.token === char['}']) break;
         closelistfield(fs, cc);
         field(ls, cc);
-    } while (testnext(ls, ',') || testnext(ls, ';'));
-    check_match(ls, '}', '{', line);
+    } while (testnext(ls, char[',']) || testnext(ls, char[';']));
+    check_match(ls, char['}'], char['{'], line);
     lastlistfield(fs, cc);
     lopcode.SETARG_B(fs.f.code[pc], lobject.luaO_int2fb(cc.na));  /* set initial array size */
     lopcode.SETARG_C(fs.f.code[pc], lobject.luaO_int2fb(cc.nh));  /* set initial table size */
@@ -735,7 +737,7 @@ const parlist = function(ls) {
     let f = fs.f;
     let nparams = 0;
     f.is_vararg = 0;
-    if (ls.t.token !== ')') {  /* is 'parlist' not empty? */
+    if (ls.t.token !== char[')']) {  /* is 'parlist' not empty? */
         do {
             switch (ls.t.token) {
                 case R.TK_NAME: {  /* param -> NAME */
@@ -750,7 +752,7 @@ const parlist = function(ls) {
                 }
                 default: llex.luaX_syntaxerror(ls, lua.to_luastring("<name> or '...' expected"));
             }
-        } while(!f.is_vararg && testnext(ls, ','));
+        } while(!f.is_vararg && testnext(ls, char[',']));
     }
     adjustlocalvars(ls, nparams);
     f.numparams = fs.nactvar;
@@ -764,13 +766,13 @@ const body = function(ls, e, ismethod, line) {
     new_fs.f = addprototype(ls);
     new_fs.f.linedefined = line;
     open_func(ls, new_fs, bl);
-    checknext(ls, '(');
+    checknext(ls, char['(']);
     if (ismethod) {
         new_localvarliteral(ls, lua.to_luastring("self"));  /* create 'self' parameter */
         adjustlocalvars(ls, 1);
     }
     parlist(ls);
-    checknext(ls, ')');
+    checknext(ls, char[')']);
     statlist(ls);
     new_fs.f.lastlinedefined = ls.linenumber;
     check_match(ls, R.TK_END, R.TK_FUNCTION, line);
@@ -782,7 +784,7 @@ const explist = function(ls, v) {
     /* explist -> expr { ',' expr } */
     let n = 1;  /* at least one expression */
     expr(ls, v);
-    while (testnext(ls, ',')) {
+    while (testnext(ls, char[','])) {
         lcode.luaK_exp2nextreg(ls.fs, v);
         expr(ls, v);
         n++;
@@ -794,18 +796,18 @@ const funcargs = function(ls, f, line) {
     let fs = ls.fs;
     let args = new expdesc();
     switch (ls.t.token) {
-        case '(': {  /* funcargs -> '(' [ explist ] ')' */
+        case char['(']: {  /* funcargs -> '(' [ explist ] ')' */
             llex.luaX_next(ls);
-            if (ls.t.token === ')')  /* arg list is empty? */
+            if (ls.t.token === char[')'])  /* arg list is empty? */
                 args.k = expkind.VVOID;
             else {
                 explist(ls, args);
                 lcode.luaK_setmultret(fs, args);
             }
-            check_match(ls, ')', '(', line);
+            check_match(ls, char[')'], char['('], line);
             break;
         }
-        case '{': {  /* funcargs -> constructor */
+        case char['{']: {  /* funcargs -> constructor */
             constructor(ls, args);
             break;
         }
@@ -842,11 +844,11 @@ const funcargs = function(ls, f, line) {
 const primaryexp = function(ls, v) {
     /* primaryexp -> NAME | '(' expr ')' */
     switch (ls.t.token) {
-        case '(': {
+        case char['(']: {
             let line = ls.linenumber;
             llex.luaX_next(ls);
             expr(ls, v);
-            check_match(ls, ')', '(', line);
+            check_match(ls, char[')'], char['('], line);
             lcode.luaK_dischargevars(ls.fs, v);
             return;
         }
@@ -868,18 +870,18 @@ const suffixedexp = function(ls, v) {
     primaryexp(ls, v);
     for (;;) {
         switch (ls.t.token) {
-            case '.': {  /* fieldsel */
+            case char['.']: {  /* fieldsel */
                 fieldsel(ls, v);
                 break;
             }
-            case '[': {  /* '[' exp1 ']' */
+            case char['[']: {  /* '[' exp1 ']' */
                 let key = new expdesc();
                 lcode.luaK_exp2anyregup(fs, v);
                 yindex(ls, key);
                 lcode.luaK_indexed(fs, v, key);
                 break;
             }
-            case ':': {  /* ':' NAME funcargs */
+            case char[':']: {  /* ':' NAME funcargs */
                 let key = new expdesc();
                 llex.luaX_next(ls);
                 checkname(ls, key);
@@ -887,7 +889,7 @@ const suffixedexp = function(ls, v) {
                 funcargs(ls, v, line);
                 break;
             }
-            case '(': case R.TK_STRING: case '{': {  /* funcargs */
+            case char['(']: case R.TK_STRING: case char['{']: {  /* funcargs */
                 lcode.luaK_exp2nextreg(fs, v);
                 funcargs(ls, v, line);
                 break;
@@ -933,7 +935,7 @@ const simpleexp = function(ls, v) {
             init_exp(v, expkind.VVARARG, lcode.luaK_codeABC(fs, OpCodesI.OP_VARARG, 0, 1, 0));
             break;
         }
-        case '{': {  /* constructor */
+        case char['{']: {  /* constructor */
             constructor(ls, v);
             return;
         }
@@ -952,34 +954,34 @@ const simpleexp = function(ls, v) {
 
 const getunopr = function(op) {
     switch (op) {
-        case R.TK_NOT: return UnOpr.OPR_NOT;
-        case '-':      return UnOpr.OPR_MINUS;
-        case '~':      return UnOpr.OPR_BNOT;
-        case '#':      return UnOpr.OPR_LEN;
-        default:       return UnOpr.OPR_NOUNOPR;
+        case R.TK_NOT:  return UnOpr.OPR_NOT;
+        case char['-']: return UnOpr.OPR_MINUS;
+        case char['~']: return UnOpr.OPR_BNOT;
+        case char['#']: return UnOpr.OPR_LEN;
+        default:        return UnOpr.OPR_NOUNOPR;
     }
 };
 
 const getbinopr = function(op) {
     switch (op) {
-        case '+':         return BinOpr.OPR_ADD;
-        case '-':         return BinOpr.OPR_SUB;
-        case '*':         return BinOpr.OPR_MUL;
-        case '%':         return BinOpr.OPR_MOD;
-        case '^':         return BinOpr.OPR_POW;
-        case '/':         return BinOpr.OPR_DIV;
+        case char['+']:   return BinOpr.OPR_ADD;
+        case char['-']:   return BinOpr.OPR_SUB;
+        case char['*']:   return BinOpr.OPR_MUL;
+        case char['%']:   return BinOpr.OPR_MOD;
+        case char['^']:   return BinOpr.OPR_POW;
+        case char['/']:   return BinOpr.OPR_DIV;
         case R.TK_IDIV:   return BinOpr.OPR_IDIV;
-        case '&':         return BinOpr.OPR_BAND;
-        case '|':         return BinOpr.OPR_BOR;
-        case '~':         return BinOpr.OPR_BXOR;
+        case char['&']:   return BinOpr.OPR_BAND;
+        case char['|']:   return BinOpr.OPR_BOR;
+        case char['~']:   return BinOpr.OPR_BXOR;
         case R.TK_SHL:    return BinOpr.OPR_SHL;
         case R.TK_SHR:    return BinOpr.OPR_SHR;
         case R.TK_CONCAT: return BinOpr.OPR_CONCAT;
         case R.TK_NE:     return BinOpr.OPR_NE;
         case R.TK_EQ:     return BinOpr.OPR_EQ;
-        case '<':         return BinOpr.OPR_LT;
+        case char['<']:   return BinOpr.OPR_LT;
         case R.TK_LE:     return BinOpr.OPR_LE;
-        case '>':         return BinOpr.OPR_GT;
+        case char['>']:   return BinOpr.OPR_GT;
         case R.TK_GE:     return BinOpr.OPR_GE;
         case R.TK_AND:    return BinOpr.OPR_AND;
         case R.TK_OR:     return BinOpr.OPR_OR;
@@ -1102,7 +1104,7 @@ const check_conflict = function(ls, lh, v) {
 const assignment = function(ls, lh, nvars) {
     let e = new expdesc();
     check_condition(ls, vkisvar(lh.v.k), lua.to_luastring("syntax error"));
-    if (testnext(ls, ',')) {  /* assignment -> ',' suffixedexp assignment */
+    if (testnext(ls, char[','])) {  /* assignment -> ',' suffixedexp assignment */
         let nv = new LHS_assign();
         nv.prev = lh;
         suffixedexp(ls, nv.v);
@@ -1111,7 +1113,7 @@ const assignment = function(ls, lh, nvars) {
         checklimit(ls.fs, nvars + ls.L.nCcalls, llimit.LUAI_MAXCCALLS, lua.to_luastring("JS levels"));
         assignment(ls, nv, nvars + 1);
     } else {  /* assignment -> '=' explist */
-        checknext(ls, '=');
+        checknext(ls, char['=']);
         let nexps = explist(ls, e);
         if (nexps !== nvars)
             adjust_assign(ls, nvars, nexps, e);
@@ -1158,7 +1160,7 @@ const checkrepeated = function(fs, ll, label) {
 
 /* skip no-op statements */
 const skipnoopstat = function(ls) {
-    while (ls.t.token === ';' || ls.t.token === R.TK_DBCOLON)
+    while (ls.t.token === char[';'] || ls.t.token === R.TK_DBCOLON)
         statement(ls);
 };
 
@@ -1256,11 +1258,11 @@ const fornum = function(ls, varname, line) {
     new_localvarliteral(ls, lua.to_luastring("(for limit)"));
     new_localvarliteral(ls, lua.to_luastring("(for step)"));
     new_localvar(ls, varname);
-    checknext(ls, '=');
+    checknext(ls, char['=']);
     exp1(ls);  /* initial value */
-    checknext(ls, ',');
+    checknext(ls, char[',']);
     exp1(ls);  /* limit */
-    if (testnext(ls, ','))
+    if (testnext(ls, char[',']))
         exp1(ls);  /* optional step */
     else {  /* default step = 1 */
         lcode.luaK_codek(fs, fs.freereg, lcode.luaK_intK(fs, 1));
@@ -1281,7 +1283,7 @@ const forlist = function(ls, indexname) {
     new_localvarliteral(ls, lua.to_luastring("(for control)"));
     /* create declared variables */
     new_localvar(ls, indexname);
-    while (testnext(ls, ',')) {
+    while (testnext(ls, char[','])) {
         new_localvar(ls, str_checkname(ls));
         nvars++;
     }
@@ -1300,8 +1302,8 @@ const forstat = function(ls, line) {
     llex.luaX_next(ls);  /* skip 'for' */
     let varname = str_checkname(ls);  /* first variable name */
     switch (ls.t.token) {
-        case '=': fornum(ls, varname, line); break;
-        case ',': case R.TK_IN: forlist(ls, varname); break;
+        case char['=']: fornum(ls, varname, line); break;
+        case char[',']: case R.TK_IN: forlist(ls, varname); break;
         default: llex.luaX_syntaxerror(ls, lua.to_luastring("'=' or 'in' expected"));
     }
     check_match(ls, R.TK_END, R.TK_FOR, line);
@@ -1373,8 +1375,8 @@ const localstat = function(ls) {
     do {
         new_localvar(ls, str_checkname(ls));
         nvars++;
-    } while (testnext(ls, ','));
-    if (testnext(ls, '='))
+    } while (testnext(ls, char[',']));
+    if (testnext(ls, char['=']))
         nexps = explist(ls, e);
     else {
         e.k = expkind.VVOID;
@@ -1388,9 +1390,9 @@ const funcname = function(ls, v) {
     /* funcname -> NAME {fieldsel} [':' NAME] */
     let ismethod = 0;
     singlevar(ls, v);
-    while (ls.t.token === '.')
+    while (ls.t.token === char['.'])
         fieldsel(ls, v);
-    if (ls.t.token === ':') {
+    if (ls.t.token === char[':']) {
         ismethod = 1;
         fieldsel(ls, v);
     }
@@ -1413,7 +1415,7 @@ const exprstat= function(ls) {
     let fs = ls.fs;
     let v = new LHS_assign();
     suffixedexp(ls, v.v);
-    if (ls.t.token === '=' || ls.t.token === ',') { /* stat . assignment ? */
+    if (ls.t.token === char['='] || ls.t.token === char[',']) { /* stat . assignment ? */
         v.prev = null;
         assignment(ls, v, 1);
     }
@@ -1428,7 +1430,7 @@ const retstat = function(ls) {
     let fs = ls.fs;
     let e = new expdesc();
     let first, nret;  /* registers with returned values */
-    if (block_follow(ls, 1) || ls.t.token === ';')
+    if (block_follow(ls, 1) || ls.t.token === char[';'])
         first = nret = 0;  /* return no values */
     else {
         nret = explist(ls, e);  /* optional return values */
@@ -1451,14 +1453,14 @@ const retstat = function(ls) {
         }
     }
     lcode.luaK_ret(fs, first, nret);
-    testnext(ls, ';');  /* skip optional semicolon */
+    testnext(ls, char[';']);  /* skip optional semicolon */
 };
 
 const statement = function(ls) {
     let line = ls.linenumber;  /* may be needed for error messages */
     enterlevel(ls);
     switch(ls.t.token) {
-        case ';': {  /* stat -> ';' (empty statement) */
+        case char[';']: {  /* stat -> ';' (empty statement) */
             llex.luaX_next(ls);  /* skip ';' */
             break;
         }
@@ -1547,7 +1549,7 @@ const luaY_parser = function(L, z, buff, dyd, name, firstchar) {
     lexstate.h = new Table();  /* create table for scanner */
     L.stack[L.top++] = lexstate.h;
     funcstate.f = cl.p = new Proto(L);
-    funcstate.f.source = new TValue(lua.CT.LUA_TLNGSTR, lua.to_luastring(name));
+    funcstate.f.source = new TValue(lua.CT.LUA_TLNGSTR, name);
     lexstate.buff = buff;
     lexstate.dyd = dyd;
     dyd.actvar.n = dyd.gt.n = dyd.label.n = 0;
diff --git a/src/lstrlib.js b/src/lstrlib.js
index 471187b..e163485 100644
--- a/src/lstrlib.js
+++ b/src/lstrlib.js
@@ -1372,7 +1372,7 @@ const createmetatable = function(L) {
     lapi.lua_setmetatable(L, -2);  /* set table as metatable for strings */
     lapi.lua_pop(L, 1);  /* pop dummy string */
     lapi.lua_pushvalue(L, -2);  /* get string library */
-    lapi.lua_setfield(L, -2, "__index");  /* metatable.__index = string */
+    lapi.lua_setfield(L, -2, lua.to_luastring("__index"));  /* metatable.__index = string */
     lapi.lua_pop(L, 1);  /* pop metatable */  
 };
 
diff --git a/src/ltablib.js b/src/ltablib.js
index c45f7e5..eaaf24d 100644
--- a/src/ltablib.js
+++ b/src/ltablib.js
@@ -163,7 +163,7 @@ const pack = function(L) {
     for (let i = n; i >= 1; i--)  /* assign elements */
         lapi.lua_seti(L, 1, i);
     lapi.lua_pushinteger(L, n);
-    lapi.lua_setfield(L, 1, "n");  /* t.n = number of elements */
+    lapi.lua_setfield(L, 1, ["n".charCodeAt(0)]);  /* t.n = number of elements */
     return 1;  /* return table */
 };
 
diff --git a/src/ltm.js b/src/ltm.js
index d2df961..4a90f6d 100644
--- a/src/ltm.js
+++ b/src/ltm.js
@@ -53,7 +53,7 @@ const luaT_typenames_ = [
     "userdata",
     "thread",
     "proto" /* this last case is used for tests only */
-];
+].map(e => lua.to_luastring(e));
 
 const ttypename = function(t) {
     return luaT_typenames_[t + 1];
diff --git a/src/lua.js b/src/lua.js
index 4710ded..85d4b64 100644
--- a/src/lua.js
+++ b/src/lua.js
@@ -135,6 +135,8 @@ class lua_Debug {
 }
 
 const to_luastring = function(str, maxBytesToWrite) {
+    assert(typeof str === "string", "to_luastring expect a js string");
+
     maxBytesToWrite = maxBytesToWrite !== undefined ? maxBytesToWrite : Number.MAX_SAFE_INTEGER;
     let outU8Array = [];
 
diff --git a/src/lundump.js b/src/lundump.js
index 7452c43..36fd674 100644
--- a/src/lundump.js
+++ b/src/lundump.js
@@ -5,10 +5,8 @@ const fs             = require('fs');
 const assert         = require('assert');
 
 const lua            = require('./lua.js');
-const LClosure       = require('./lobject.js').LClosure;
-const TValue         = require('./lobject.js').TValue;
+const lobject        = require('./lobject.js');
 const Proto          = require('./lfunc.js').Proto;
-const constant_types = require('./lua.js').constant_types;
 const OpCodes        = require('./lopcodes.js');
 
 const LUAI_MAXSHORTLEN = 40;
@@ -167,20 +165,20 @@ class BytecodeParser {
             let t = this.readByte();
 
             switch (t) {
-            case constant_types.LUA_TNIL:
-                f.k.push(new TValue(constant_types.LUA_TNIL, null));
+            case lua.CT.LUA_TNIL:
+                f.k.push(new lobject.TValue(lua.CT.LUA_TNIL, null));
                 break;
-            case constant_types.LUA_TBOOLEAN:
-                f.k.push(new TValue(constant_types.LUA_TBOOLEAN, this.readByte()));
+            case lua.CT.LUA_TBOOLEAN:
+                f.k.push(new lobject.TValue(lua.CT.LUA_TBOOLEAN, this.readByte()));
                 break;
-            case constant_types.LUA_TNUMFLT:
-                f.k.push(new TValue(constant_types.LUA_TNUMFLT, this.readNumber()));
+            case lua.CT.LUA_TNUMFLT:
+                f.k.push(new lobject.TValue(lua.CT.LUA_TNUMFLT, this.readNumber()));
                 break;
-            case constant_types.LUA_TNUMINT:
-                f.k.push(new TValue(constant_types.LUA_TNUMINT, this.readInteger()));
+            case lua.CT.LUA_TNUMINT:
+                f.k.push(new lobject.TValue(lua.CT.LUA_TNUMINT, this.readInteger()));
                 break;
-            case constant_types.LUA_TSHRSTR:
-            case constant_types.LUA_TLNGSTR:
+            case lua.CT.LUA_TSHRSTR:
+            case lua.CT.LUA_TLNGSTR:
                 f.k.push(this.L.l_G.intern(this.read8bitString()));
                 break;
             default:
@@ -206,7 +204,7 @@ class BytecodeParser {
         n = this.readInt();
         for (let i = 0; i < n; i++) {
             f.locvars[i] = {
-                varname: this.readString(),
+                varname: new lobject.TValue(lua.CT.LUA_TLNGSTR, lua.to_luastring(this.readString())),
                 startpc: this.readInt(),
                 endpc:   this.readInt()
             };
@@ -264,7 +262,7 @@ class BytecodeParser {
     luaU_undump() {
         this.checkHeader();
 
-        let cl = new LClosure(this.L, this.readByte());
+        let cl = new lobject.LClosure(this.L, this.readByte());
 
         this.L.stack[this.L.top] = cl;
         this.L.top++;
@@ -280,4 +278,4 @@ class BytecodeParser {
 
 }
 
-module.exports = BytecodeParser;
\ No newline at end of file
+module.exports = BytecodeParser;
diff --git a/src/lutf8lib.js b/src/lutf8lib.js
index 1df6096..ef9739f 100644
--- a/src/lutf8lib.js
+++ b/src/lutf8lib.js
@@ -58,50 +58,37 @@ const utf8_decode = function(s, val) {
 ** range [i,j], or nil + current position if 's' is not well formed in
 ** that interval
 */
-// const utflen = function(L) {
-//     let n = 0;
-//     let s = lauxlib.luaL_checkstring(L, 1);
-//     s = L.stack[lapi.index2addr_(L, 1)].value;
-//     let len = s.length;
-//     let posi = u_posrelat(lauxlib.luaL_optinteger(L, 2, 1), len);
-//     let posj = u_posrelat(lauxlib.luaL_optinteger(L, 3, -1), len);
-//
-//     lauxlib.luaL_argcheck(L, 1 <= posi && --posi <= len, 2, "initial position out of string");
-//     lauxlib.luaL_argcheck(L, --posj < len, 3, "final position out of string");
-//
-//     while (posi <= posj) {
-//         let dec = utf8_decode(s[posi]);
-//         let s1 = dec ? dec.string : null;
-//         if (s1 === null) {
-//             /* conversion error? */
-//             lapi.lua_pushnil(L);  /* return nil ... */
-//             lapi.lua_pushinteger(L, posi + 1);  /* ... and current position */
-//             return 2;
-//         }
-//         posi = dec.pos;
-//         n++;
-//     }
-//     lapi.lua_pushinteger(L, n);
-//     return 1;
-// };
-
-// Shorter JSesque solution but doesn't take invalid UTF-8 sequence (but how can we get one ?)
 const utflen = function(L) {
+    let n = 0;
     let s = lauxlib.luaL_checkstring(L, 1);
-    let posi = u_posrelat(lauxlib.luaL_optinteger(L, 2, 1), s.length);
-    let posj = u_posrelat(lauxlib.luaL_optinteger(L, 3, -1), s.length);
-
-    lauxlib.luaL_argcheck(L, 1 <= posi && --posi <= s.length, 2, lua.to_luastring("initial position out of string"));
-    lauxlib.luaL_argcheck(L, --posj < s.length, 3, lua.to_luastring("final position out of string"));
-
-    lapi.lua_pushinteger(L, s.slice(posi, posj + 1).length);
+    s = L.stack[lapi.index2addr_(L, 1)].value;
+    let len = s.length;
+    let posi = u_posrelat(lauxlib.luaL_optinteger(L, 2, 1), len);
+    let posj = u_posrelat(lauxlib.luaL_optinteger(L, 3, -1), len);
+
+    lauxlib.luaL_argcheck(L, 1 <= posi && --posi <= len, 2, "initial position out of string");
+    lauxlib.luaL_argcheck(L, --posj < len, 3, "final position out of string");
+
+    while (posi <= posj) {
+        let dec = utf8_decode(s.slice(posi));
+        let s1 = dec ? dec.string : null;
+        if (s1 === null) {
+            /* conversion error? */
+            lapi.lua_pushnil(L);  /* return nil ... */
+            lapi.lua_pushinteger(L, posi + 1);  /* ... and current position */
+            return 2;
+        }
+        posi = s.length - s1.length;
+        n++;
+    }
+    lapi.lua_pushinteger(L, n);
     return 1;
 };
 
 const pushutfchar = function(L, arg) {
     let code = lauxlib.luaL_checkinteger(L, arg);
     lauxlib.luaL_argcheck(L, 0 <= code && code <= MAXUNICODE, arg, lua.to_luastring("value out of range"));
-    lapi.lua_pushstring(L, `${String.fromCharCode(code)}`);
+    lapi.lua_pushstring(L, lua.to_luastring(String.fromCharCode(code)));
 };
 
 /*
@@ -248,8 +235,8 @@ const UTF8PATT = "[\0-\x7F\xC2-\xF4][\x80-\xBF]*";
 
 const luaopen_utf8 = function(L) {
     lauxlib.luaL_newlib(L, funcs);
-    lapi.lua_pushstring(L, UTF8PATT);
-    lapi.lua_setfield(L, -2, "charpattern");
+    lapi.lua_pushstring(L, lua.to_luastring(UTF8PATT));
+    lapi.lua_setfield(L, -2, lua.to_luastring("charpattern"));
     return 1;
 };
 
diff --git a/src/lvm.js b/src/lvm.js
index 53e1584..6f49ad3 100644
--- a/src/lvm.js
+++ b/src/lvm.js
@@ -592,19 +592,19 @@ const luaV_execute = function(L) {
                     let nstep = tonumber(pstep);
 
                     if (nlimit === false)
-                        ldebug.luaG_runerror(L, "'for' limit must be a number");
+                        ldebug.luaG_runerror(L, lua.to_luastring("'for' limit must be a number"));
 
                     plimit.type = CT.LUA_TNUMFLT;
                     plimit.value = nlimit;
 
                     if (nstep === false)
-                        ldebug.luaG_runerror(L, "'for' step must be a number");
+                        ldebug.luaG_runerror(L, lua.to_luastring("'for' step must be a number"));
 
                     pstep.type = CT.LUA_TNUMFLT;
                     pstep.value = nstep;
 
                     if (ninit === false)
-                        ldebug.luaG_runerror(L, "'for' initial value must be a number");
+                        ldebug.luaG_runerror(L, lua.to_luastring("'for' initial value must be a number"));
 
                     init.type = CT.LUA_TNUMFLT;
                     init.value = ninit - nstep;
@@ -977,7 +977,7 @@ const luaV_objlen = function(L, ra, rb) {
         default: {
             tm = ltm.luaT_gettmbyobj(L, rb, ltm.TMS.TM_LEN);
             if (tm.ttisnil())
-                ldebug.luaG_typeerror(L, rb, "get length of");
+                ldebug.luaG_typeerror(L, rb, lua.to_luastring("get length of"));
             break;
         }
     }
@@ -1042,7 +1042,7 @@ const gettable = function(L, table, key, ra, recur) {
     recur = recur ? recur : 0;
 
     if (recur >= MAXTAGRECUR)
-        ldebug.luaG_runerror(L, "'__index' chain too long; possible loop");
+        ldebug.luaG_runerror(L, lua.to_luastring("'__index' chain too long; possible loop"));
 
     if (table.ttistable()) {
         let element = table.__index(table, key);
@@ -1063,7 +1063,7 @@ const luaV_finishget = function(L, t, key, val, slot, recur) {
         assert(!t.ttistable());
         tm = ltm.luaT_gettmbyobj(L, t, ltm.TMS.TM_INDEX);
         if (tm.ttisnil())
-            ldebug.luaG_typeerror(L, t, 'index');
+            ldebug.luaG_typeerror(L, t, lua.to_luastring('index'));
     } else { /* 't' is a table */
         assert(slot.ttisnil());
         tm = ltm.luaT_gettmbyobj(L, t, ltm.TMS.TM_INDEX); // TODO: fasttm
@@ -1085,7 +1085,7 @@ const settable = function(L, table, key, v, recur) {
     recur = recur ? recur : 0;
 
     if (recur >= MAXTAGRECUR)
-        ldebug.luaG_runerror(L, "'__newindex' chain too long; possible loop");
+        ldebug.luaG_runerror(L, lua.to_luastring("'__newindex' chain too long; possible loop"));
 
     if (table.ttistable()) {
         let element = table.__index(table, key);
@@ -1112,7 +1112,7 @@ const luaV_finishset = function(L, t, key, val, slot, recur) {
     } else { /* not a table; check metamethod */
         tm = ltm.luaT_gettmbyobj(L, t, ltm.TMS.TM_NEWINDEX);
         if (tm.ttisnil())
-            ldebug.luaG_typeerror(L, t, 'index');
+            ldebug.luaG_typeerror(L, t, lua.to_luastring('index'));
     }
 
     if (tm.ttisfunction()) {