performance: create a fast path for parsing names without special characters

Author: fabiosantoscode

lib/parse.js

@@ -548,15 +548,16 @@ function tokenizer($TEXT, filename, html5_comments, shebang) {
                 return after_e;
               case (after_e = false, 46): // .
                 return (!has_dot && !has_x && !has_e) ? (has_dot = true) : false;
-            }
-
-            if (ch === "n") {
+              case 110: // n
                 is_big_int = true;
-
                 return true;
             }
 
-            return RE_NUM_LITERAL.test(ch);
+            return (
+                code >= 48 && code <= 57 // 0-9
+                || code >= 97 && code <= 102 // a-f
+                || code >= 65 && code <= 70 // A-F
+            );
         });
         if (prefix) num = prefix + num;
 
@@ -573,7 +574,7 @@ function tokenizer($TEXT, filename, html5_comments, shebang) {
             }
             num = num.replace(/_/g, "");
         }
-        if (num.endsWith("n")) {
+        if (is_big_int) {
             const without_n = num.slice(0, -1);
             const allow_e = RE_HEX_NUMBER.test(without_n);
             const valid = parse_js_number(without_n, allow_e);
@@ -748,7 +749,24 @@ function tokenizer($TEXT, filename, html5_comments, shebang) {
         return next_token;
     });
 
-    var read_name = with_eof_error("Unterminated identifier name", function() {
+    var read_name = function () {
+        let start = S.pos, end = start - 1, ch = 'c';
+
+        while (
+            (ch = S.text.charAt(++end))
+            && (ch >= 'a' && ch <= 'z' || ch >= 'A' && ch <= 'Z')
+        );
+
+        if (end > start + 1 && ch && ch !== '\\' && !is_identifier_char(ch)) {
+            S.pos += end - start;
+            S.col += end - start;
+            return S.text.slice(start, S.pos);
+        }
+
+        return read_name_hard();
+    };
+
+    var read_name_hard = with_eof_error("Unterminated identifier name", function() {
         var name = [], ch, escaped = false;
         var read_escaped_identifier_char = function() {
             escaped = true;