minifier: inline String.fromCharCode() with ints

evanw · Oct 17, 2023 · 126ca5a · 126ca5a
1 parent 6d20a48
commit 126ca5a
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -1,5 +1,22 @@
 # Changelog
 
+## Unreleased
+
+* Add some improvements to the JavaScript minifier
+
+    This release adds more cases to the JavaScript minifier, including support for inlining `String.fromCharCode` and `String.prototype.charCodeAt` when possible:
+
+    ```js
+    // Original code
+    document.onkeydown = e => e.keyCode === 'A'.charCodeAt(0) && console.log(String.fromCharCode(55358, 56768))
+
+    // Old output (with --minify)
+    document.onkeydown=o=>o.keyCode==="A".charCodeAt(0)&&console.log(String.fromCharCode(55358,56768));
+
+    // New output (with --minify)
+    document.onkeydown=o=>o.keyCode===65&&console.log("🧀");
+    ```
+
 ## 0.19.5
 
 * Fix a regression in 0.19.0 regarding `paths` in `tsconfig.json` ([#3354](https://github.com/evanw/esbuild/issues/3354))

diff --git a/internal/js_parser/js_parser.go b/internal/js_parser/js_parser.go
@@ -14554,9 +14554,9 @@ func (p *parser) visitExprInOut(expr js_ast.Expr, in exprIn) (js_ast.Expr, exprO
 				}
 			}
 
-			// Recognize "charCodeAt()" calls
-			if p.options.minifySyntax && len(e.Args) <= 1 {
-				if t.Name == "charCodeAt" {
+			if p.options.minifySyntax {
+				if len(e.Args) <= 1 && t.Name == "charCodeAt" {
+					// Recognize "charCodeAt()" calls
 					if str, ok := t.Target.Data.(*js_ast.EString); ok {
 						index := 0
 						hasIndex := false
@@ -14574,6 +14574,23 @@ func (p *parser) visitExprInOut(expr js_ast.Expr, in exprIn) (js_ast.Expr, exprO
 							}
 						}
 					}
+				} else if t.Name == "fromCharCode" {
+					// Recognize "fromCharCode()" calls
+					if id, ok := t.Target.Data.(*js_ast.EIdentifier); ok {
+						if symbol := &p.symbols[id.Ref.InnerIndex]; symbol.Kind == ast.SymbolUnbound && symbol.OriginalName == "String" {
+							charCodes := make([]uint16, 0, len(e.Args))
+							for _, arg := range e.Args {
+								arg, ok := js_ast.ToNumberWithoutSideEffects(arg.Data)
+								if !ok {
+									break
+								}
+								charCodes = append(charCodes, uint16(js_ast.ToInt32(arg)))
+							}
+							if len(charCodes) == len(e.Args) {
+								return js_ast.Expr{Loc: expr.Loc, Data: &js_ast.EString{Value: charCodes}}, exprOut{}
+							}
+						}
+					}
 				}
 			}
 

diff --git a/internal/js_parser/js_parser_test.go b/internal/js_parser/js_parser_test.go
@@ -3581,6 +3581,26 @@ func TestMangleCharCodeAt(t *testing.T) {
 	expectPrintedMangle(t, "a = 'xy'.charCodeAt(1, 2)", "a = \"xy\".charCodeAt(1, 2);\n")
 }
 
+func TestMangleFromCharCode(t *testing.T) {
+	expectPrinted(t, "a = String.fromCharCode(120, 121)", "a = String.fromCharCode(120, 121);\n")
+
+	expectPrintedMangle(t, "a = String.fromCharCode()", "a = \"\";\n")
+	expectPrintedMangle(t, "a = String.fromCharCode(0)", "a = \"\\0\";\n")
+	expectPrintedMangle(t, "a = String.fromCharCode(120)", "a = \"x\";\n")
+	expectPrintedMangle(t, "a = String.fromCharCode(120, 121)", "a = \"xy\";\n")
+	expectPrintedMangle(t, "a = String.fromCharCode(55358, 56768)", "a = \"🧀\";\n")
+	expectPrintedMangle(t, "a = String.fromCharCode(0x10000)", "a = \"\\0\";\n")
+	expectPrintedMangle(t, "a = String.fromCharCode(0x10078, 0x10079)", "a = \"xy\";\n")
+	expectPrintedMangle(t, "a = String.fromCharCode(0x1_0000_FFFF)", "a = \"\uFFFF\";\n")
+	expectPrintedMangle(t, "a = String.fromCharCode(NaN)", "a = \"\\0\";\n")
+	expectPrintedMangle(t, "a = String.fromCharCode(Infinity)", "a = \"\\0\";\n")
+	expectPrintedMangle(t, "a = String.fromCharCode(null)", "a = \"\\0\";\n")
+	expectPrintedMangle(t, "a = String.fromCharCode(undefined)", "a = \"\\0\";\n")
+
+	expectPrintedMangle(t, "a = String.fromCharCode(x)", "a = String.fromCharCode(x);\n")
+	expectPrintedMangle(t, "a = String.fromCharCode('123')", "a = String.fromCharCode(\"123\");\n")
+}
+
 func TestMangleIf(t *testing.T) {
 	expectPrintedNormalAndMangle(t, "1 ? a() : b()", "1 ? a() : b();\n", "a();\n")
 	expectPrintedNormalAndMangle(t, "0 ? a() : b()", "0 ? a() : b();\n", "b();\n")

diff --git a/scripts/end-to-end-tests.js b/scripts/end-to-end-tests.js
@@ -3242,7 +3242,7 @@ for (const minify of [[], ['--minify-syntax']]) {
       test(['in.js', '--outfile=node.js', '--log-level=error'].concat(minify), {
         'in.js': `if ({a: 1, a: 2}${access} !== 2) throw 'fail'`,
       }),
-      test(['in.js', '--outfile=node.js'].concat(minify), {
+      test(['in.js', '--outfile=node.js', '--log-level=error'].concat(minify), {
         'in.js': `if ({a: 1, [String.fromCharCode(97)]: 2}${access} !== 2) throw 'fail'`,
       }),
       test(['in.js', '--outfile=node.js'].concat(minify), {