perf: replace lookahead by lookaheadCharCode

babel · Aug 28, 2019 · 23a29b6 · 23a29b6
1 parent 94e47c3
commit 23a29b6
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Showing 4 changed files with 23 additions and 6 deletions.
diff --git a/packages/babel-parser/src/parser/expression.js b/packages/babel-parser/src/parser/expression.js
@@ -590,7 +590,7 @@ export default class ExpressionParser extends LValParser {
     } else if (this.match(tt.questionDot)) {
       this.expectPlugin("optionalChaining");
       state.optionalChainMember = true;
-      if (noCalls && this.lookahead().type === tt.parenL) {
+      if (noCalls && this.lookaheadCharCode() === charCodes.leftParenthesis) {
         state.stop = true;
         return base;
       }

diff --git a/packages/babel-parser/src/parser/statement.js b/packages/babel-parser/src/parser/statement.js
@@ -170,7 +170,7 @@ export default class StatementParser extends ExpressionParser {
       case tt._for:
         return this.parseForStatement(node);
       case tt._function:
-        if (this.lookahead().type === tt.dot) break;
+        if (this.lookaheadCharCode() === charCodes.dot) break;
         if (context) {
           if (this.state.strict) {
             this.raise(
@@ -223,8 +223,11 @@ export default class StatementParser extends ExpressionParser {
         return this.parseEmptyStatement(node);
       case tt._export:
       case tt._import: {
-        const nextToken = this.lookahead();
-        if (nextToken.type === tt.parenL || nextToken.type === tt.dot) {
+        const nextTokenCharCode = this.lookaheadCharCode();
+        if (
+          nextTokenCharCode === charCodes.leftParenthesis ||
+          nextTokenCharCode === charCodes.dot
+        ) {
           break;
         }
 

diff --git a/packages/babel-parser/src/plugins/typescript/index.js b/packages/babel-parser/src/plugins/typescript/index.js
@@ -19,6 +19,7 @@ import {
   BIND_CLASS,
 } from "../../util/scopeflags";
 import TypeScriptScopeHandler from "./scope";
+import * as charCodes from "charcodes";
 
 type TsModifier =
   | "readonly"
@@ -657,7 +658,10 @@ export default (superClass: Class<Parser>): Class<Parser> =>
             : this.match(tt._null)
             ? "TSNullKeyword"
             : keywordTypeFromName(this.state.value);
-          if (type !== undefined && this.lookahead().type !== tt.dot) {
+          if (
+            type !== undefined &&
+            this.lookaheadCharCode() !== charCodes.dot
+          ) {
             const node: N.TsKeywordType = this.startNode();
             this.next();
             return this.finishNode(node, type);
@@ -1203,7 +1207,8 @@ export default (superClass: Class<Parser>): Class<Parser> =>
 
     tsIsExternalModuleReference(): boolean {
       return (
-        this.isContextual("require") && this.lookahead().type === tt.parenL
+        this.isContextual("require") &&
+        this.lookaheadCharCode() === charCodes.leftParenthesis
       );
     }
 

diff --git a/packages/babel-parser/src/tokenizer/index.js b/packages/babel-parser/src/tokenizer/index.js
@@ -17,6 +17,7 @@ import {
 import State from "./state";
 
 const VALID_REGEX_FLAGS = new Set(["g", "m", "s", "i", "y", "u"]);
+const skipWhiteSpace = /(?:\s|\/\/.*|\/\*[^]*?\*\/)*/g;
 
 // The following character codes are forbidden from being
 // an immediate sibling of NumericLiteralSeparator _
@@ -168,6 +169,14 @@ export default class Tokenizer extends LocationParser {
     return curr;
   }
 
+  lookaheadCharCode(): number {
+    const thisTokEnd = this.state.pos;
+    skipWhiteSpace.lastIndex = thisTokEnd;
+    const skip = skipWhiteSpace.exec(this.input);
+    const next = thisTokEnd + skip[0].length;
+    return this.input.charCodeAt(next);
+  }
+
   // Toggle strict mode. Re-reads the next number or string to please
   // pedantic tests (`"use strict"; 010;` should fail).