Emit Arrow function natively in ES6

Yui T · Yui T · commit b0ea40164ce3 · 2015-01-06T18:18:37.000-08:00
diff --git a/src/compiler/emitter.ts b/src/compiler/emitter.ts
@@ -3219,7 +3219,15 @@ module ts {
                     // Methods will emit the comments as part of emitting method declaration
                     emitLeadingComments(node);
                 }
-                write("function ");
+
+                if (node.kind !== SyntaxKind.ArrowFunction) {
+                    write("function ");
+                }
+                else if (node.kind === SyntaxKind.ArrowFunction && compilerOptions.target < ScriptTarget.ES6) {
+                    // When targeting ES6, emit arrow function natively in ES6 by omitting function keyword and using fat arrow instead
+                    write("function ");
+                }
+
                 if (node.kind === SyntaxKind.FunctionDeclaration || (node.kind === SyntaxKind.FunctionExpression && node.name)) {
                     emit(node.name);
                 }
@@ -3258,6 +3266,12 @@ module ts {
                 tempVariables = undefined;
                 tempParameters = undefined;
                 emitSignatureParameters(node);
+
+                // When targeting ES6, emit arrow function natively in ES6
+                if (node.kind === SyntaxKind.ArrowFunction && compilerOptions.target >= ScriptTarget.ES6) {
+                   write(" => ");
+                }
+
                 write(" {");
                 scopeEmitStart(node);
                 increaseIndent();
diff --git a/src/harness/projectsRunner.ts b/src/harness/projectsRunner.ts
@@ -165,7 +165,7 @@ class ProjectRunner extends RunnerBase {
                     sourceRoot: testCase.resolveSourceRoot && testCase.sourceRoot ? ts.sys.resolvePath(testCase.sourceRoot) : testCase.sourceRoot,
                     module: moduleKind,
                     noResolve: testCase.noResolve,
-                    target: ts.ScriptTarget.ES6
+                    target: ts.ScriptTarget.Latest
                 };
             }
 
diff --git a/tests/baselines/reference/constDeclarations-scopes.js b/tests/baselines/reference/constDeclarations-scopes.js
@@ -220,7 +220,7 @@ function F() {
     const c = 0;
     n = c;
 }
-var F2 = function () {
+var F2 = () =>  {
     const c = 0;
     n = c;
 };
@@ -269,7 +269,7 @@ var o = {
         const c = 0;
         n = c;
     },
-    f2: function () {
+    f2: () =>  {
         const c = 0;
         n = c;
     }
diff --git a/tests/baselines/reference/constDeclarations-validContexts.js b/tests/baselines/reference/constDeclarations-validContexts.js
@@ -183,7 +183,7 @@ const c18 = 0;
 function F() {
     const c19 = 0;
 }
-var F2 = function () {
+var F2 = () =>  {
     const c20 = 0;
 };
 var F3 = function () {
@@ -223,7 +223,7 @@ var o = {
     f() {
         const c28 = 0;
     },
-    f2: function () {
+    f2: () =>  {
         const c29 = 0;
     }
 };
diff --git a/tests/baselines/reference/letDeclarations-scopes.js b/tests/baselines/reference/letDeclarations-scopes.js
@@ -236,7 +236,7 @@ function F() {
     let l = 0;
     n = l;
 }
-var F2 = function () {
+var F2 = () =>  {
     let l = 0;
     n = l;
 };
@@ -286,7 +286,7 @@ var o = {
         let l = 0;
         n = l;
     },
-    f2: function () {
+    f2: () =>  {
         let l = 0;
         n = l;
     }
diff --git a/tests/baselines/reference/letDeclarations-validContexts.js b/tests/baselines/reference/letDeclarations-validContexts.js
@@ -203,7 +203,7 @@ let l18 = 0;
 function F() {
     let l19 = 0;
 }
-var F2 = function () {
+var F2 = () =>  {
     let l20 = 0;
 };
 var F3 = function () {
@@ -243,7 +243,7 @@ var o = {
     f() {
         let l28 = 0;
     },
-    f2: function () {
+    f2: () =>  {
         let l29 = 0;
     }
 };
diff --git a/tests/baselines/reference/project/prologueEmit/amd/out.js b/tests/baselines/reference/project/prologueEmit/amd/out.js
@@ -1,6 +1,6 @@
 var _this = this;
 // Add a lambda to ensure global 'this' capture is triggered
-(function () { return _this.window; });
+(() =>  { return _this.window; });
 var __extends = this.__extends || function (d, b) {
     for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p];
     function __() { this.constructor = d; }
diff --git a/tests/baselines/reference/project/prologueEmit/node/out.js b/tests/baselines/reference/project/prologueEmit/node/out.js
@@ -1,6 +1,6 @@
 var _this = this;
 // Add a lambda to ensure global 'this' capture is triggered
-(function () { return _this.window; });
+(() =>  { return _this.window; });
 var __extends = this.__extends || function (d, b) {
     for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p];
     function __() { this.constructor = d; }
diff --git a/tests/baselines/reference/taggedTemplateStringsTypeArgumentInferenceES6.js b/tests/baselines/reference/taggedTemplateStringsTypeArgumentInferenceES6.js
@@ -111,40 +111,40 @@ someGenerics1b `${3}`;
 // Generic tag with argument of function type whose parameter is of type parameter type
 function someGenerics2a(strs, n) {
 }
-someGenerics2a `${function (n) { return n; }}`;
+someGenerics2a `${(n) =>  { return n; }}`;
 function someGenerics2b(strs, n) {
 }
-someGenerics2b `${function (n, x) { return n; }}`;
+someGenerics2b `${(n, x) =>  { return n; }}`;
 // Generic tag with argument of function type whose parameter is not of type parameter type but body/return type uses type parameter
 function someGenerics3(strs, producer) {
 }
-someGenerics3 `${function () { return ''; }}`;
-someGenerics3 `${function () { return undefined; }}`;
-someGenerics3 `${function () { return 3; }}`;
+someGenerics3 `${() =>  { return ''; }}`;
+someGenerics3 `${() =>  { return undefined; }}`;
+someGenerics3 `${() =>  { return 3; }}`;
 // 2 parameter generic tag with argument 1 of type parameter type and argument 2 of function type whose parameter is of type parameter type
 function someGenerics4(strs, n, f) {
 }
-someGenerics4 `${4}${function () { return null; }}`;
-someGenerics4 `${''}${function () { return 3; }}`;
+someGenerics4 `${4}${() =>  { return null; }}`;
+someGenerics4 `${''}${() =>  { return 3; }}`;
 someGenerics4 `${null}${null}`;
 // 2 parameter generic tag with argument 2 of type parameter type and argument 1 of function type whose parameter is of type parameter type
 function someGenerics5(strs, n, f) {
 }
-someGenerics5 `${4} ${function () { return null; }}`;
-someGenerics5 `${''}${function () { return 3; }}`;
+someGenerics5 `${4} ${() =>  { return null; }}`;
+someGenerics5 `${''}${() =>  { return 3; }}`;
 someGenerics5 `${null}${null}`;
 // Generic tag with multiple arguments of function types that each have parameters of the same generic type
 function someGenerics6(strs, a, b, c) {
 }
-someGenerics6 `${function (n) { return n; }}${function (n) { return n; }}${function (n) { return n; }}`;
-someGenerics6 `${function (n) { return n; }}${function (n) { return n; }}${function (n) { return n; }}`;
-someGenerics6 `${function (n) { return n; }}${function (n) { return n; }}${function (n) { return n; }}`;
+someGenerics6 `${(n) =>  { return n; }}${(n) =>  { return n; }}${(n) =>  { return n; }}`;
+someGenerics6 `${(n) =>  { return n; }}${(n) =>  { return n; }}${(n) =>  { return n; }}`;
+someGenerics6 `${(n) =>  { return n; }}${(n) =>  { return n; }}${(n) =>  { return n; }}`;
 // Generic tag with multiple arguments of function types that each have parameters of different generic type
 function someGenerics7(strs, a, b, c) {
 }
-someGenerics7 `${function (n) { return n; }}${function (n) { return n; }}${function (n) { return n; }}`;
-someGenerics7 `${function (n) { return n; }}${function (n) { return n; }}${function (n) { return n; }}`;
-someGenerics7 `${function (n) { return n; }}${function (n) { return n; }}${function (n) { return n; }}`;
+someGenerics7 `${(n) =>  { return n; }}${(n) =>  { return n; }}${(n) =>  { return n; }}`;
+someGenerics7 `${(n) =>  { return n; }}${(n) =>  { return n; }}${(n) =>  { return n; }}`;
+someGenerics7 `${(n) =>  { return n; }}${(n) =>  { return n; }}${(n) =>  { return n; }}`;
 // Generic tag with argument of generic function type
 function someGenerics8(strs, n) {
     return n;
diff --git a/tests/baselines/reference/taggedTemplateStringsWithOverloadResolution3_ES6.js b/tests/baselines/reference/taggedTemplateStringsWithOverloadResolution3_ES6.js
@@ -118,5 +118,5 @@ fn4 `${null}${true}`;
 function fn5() {
     return undefined;
 }
-fn5 `${function (n) { return n.toFixed(); }}`; // will error; 'n' should have type 'string'.
-fn5 `${function (n) { return n.substr(0); }}`;
+fn5 `${(n) =>  { return n.toFixed(); }}`; // will error; 'n' should have type 'string'.
+fn5 `${(n) =>  { return n.substr(0); }}`;
diff --git a/tests/baselines/reference/templateStringInArrowFunctionES6.js b/tests/baselines/reference/templateStringInArrowFunctionES6.js
@@ -2,4 +2,4 @@
 var x = x => `abc${ x }def`;
 
 //// [templateStringInArrowFunctionES6.js]
-var x = function (x) { return `abc${x}def`; };
+var x = (x) =>  { return `abc${x}def`; };
diff --git a/tests/baselines/reference/templateStringWithEmbeddedArrowFunctionES6.js b/tests/baselines/reference/templateStringWithEmbeddedArrowFunctionES6.js
@@ -2,4 +2,4 @@
 var x = `abc${ x => x }def`;
 
 //// [templateStringWithEmbeddedArrowFunctionES6.js]
-var x = `abc${function (x) { return x; }}def`;
+var x = `abc${(x) =>  { return x; }}def`;

Original file line number	Diff line number	Diff line change
`@@ -165,7 +165,7 @@ class ProjectRunner extends RunnerBase {`
`165`	`165`	`sourceRoot: testCase.resolveSourceRoot && testCase.sourceRoot ? ts.sys.resolvePath(testCase.sourceRoot) : testCase.sourceRoot,`
`166`	`166`	`module: moduleKind,`
`167`	`167`	`noResolve: testCase.noResolve,`
`168`		`- target: ts.ScriptTarget.ES6`
	`168`	`+ target: ts.ScriptTarget.Latest`
`169`	`169`	`};`
`170`	`170`	`}`
`171`	`171`
Original file line number	Diff line number	Diff line change
@@ -118,5 +118,5 @@ fn4 `${null}${true}`;
`118`	`118`	`function fn5() {`
`119`	`119`	`return undefined;`
`120`	`120`	`}`
`121`		-fn5 `${function (n) { return n.toFixed(); }}`; // will error; 'n' should have type 'string'.
`122`		-fn5 `${function (n) { return n.substr(0); }}`;
	`121`	+fn5 `${(n) => { return n.toFixed(); }}`; // will error; 'n' should have type 'string'.
	`122`	+fn5 `${(n) => { return n.substr(0); }}`;