dry up array comprehension and arrow functions by introducing an alias-functions transformer

lib/6to5/transform.js

@@ -31,15 +31,13 @@ transform.test = function (task, assert) {
   actualCode       = recast.prettyPrint(actualAst).code;
 
   if (task.options.exec) {
-    try {
     var fn = new Function("assert", actualCode);
     fn(assert);
-    } catch (err) {
-      console.log(actualCode);
-      throw err;
   }
-  } else {
+
   var expectCode = expect.code.trim();
+
+  if (!task.options.exec || (task.options.exec && expectCode)) {
     var expectAst    = util.parse(expect, expectCode);
     var expectResult = recast.prettyPrint(expectAst);
     expectCode       = expectResult.code;
@@ -64,7 +62,7 @@ transform.test = function (task, assert) {
 
 transform._ensureTransformerNames = function (type, keys) {
   _.each(keys, function (key) {
-    if (!transform.transformers[key]) {
+    if (key[0] === "_" || !transform.transformers[key]) {
       throw new ReferenceError("unknown transformer " + key + " specified in " + type);
     }
   });
@@ -87,5 +85,7 @@ transform.transformers = {
   restParameters:           require("./transformers/rest-parameters"),
   destructuring:            require("./transformers/destructuring"),
   forOf:                    require("./transformers/for-of"),
-  unicodeRegex:             require("./transformers/unicode-regex")
+  unicodeRegex:             require("./transformers/unicode-regex"),
+
+  _aliasFunctions:          require("./transformers/_alias-functions")
 };

lib/6to5/transformers/_alias-functions.js

@@ -0,0 +1,77 @@
+var traverse = require("../traverse");
+var util     = require("../util");
+var b        = require("ast-types").builders;
+
+var go = function (getBody, node, file) {
+  var argumentsId;
+  var thisId;
+
+  var getArgumentsId = function () {
+    return argumentsId = argumentsId || b.identifier(file.generateUid("arguments"));
+  };
+
+  var getThisId = function () {
+    return thisId = thisId || b.identifier(file.generateUid("this"));
+  };
+
+  // traverse the function and find all alias functions so we can alias
+  // arguments and this if neccesary
+  traverse(node, function (node) {
+    if (!node._aliasFunction) {
+      if (traverse.isFunction(node)) {
+        // stop traversal of this node as it'll be hit again by this transformer
+        return false;
+      } else {
+        return;
+      }
+    }
+
+    // traverse all child nodes of this function and find arguments and this
+    traverse(node, function (node, parent) {
+      var getId;
+
+      if (node.type === "Identifier" && node.name === "arguments") {
+        getId = getArgumentsId;
+      } else if (node.type === "ThisExpression") {
+        getId = getThisId;
+      } else {
+        return;
+      }
+
+      if (util.isReferenced(node, parent)) return getId();
+    }, node._aliasFunctionStopNonArrowFunctions && ["FunctionExpression", "FunctionDeclaration"]);
+
+    return false;
+  });
+
+  var body;
+
+  var pushDeclaration = function (id, init) {
+    body = body || getBody();
+    body.unshift(b.variableDeclaration("var", [
+      b.variableDeclarator(id, init)
+    ]));
+  };
+
+  if (argumentsId) {
+    pushDeclaration(argumentsId, b.identifier("arguments"));
+  }
+
+  if (thisId) {
+    pushDeclaration(thisId, b.identifier("this"));
+  }
+};
+
+exports.Program = function (node, parent, file) {
+  go(function () {
+    return node.body;
+  }, node, file);
+};
+
+exports.FunctionDeclaration =
+exports.FunctionExpression = function (node, parent, file) {
+  go(function () {
+    util.ensureBlock(node);
+    return node.body.body;
+  }, node, file);
+};

lib/6to5/transformers/array-comprehension.js

@@ -9,12 +9,14 @@ var single = function (node) {
   var templateName = "array-comprehension-map";
   if (node.filter) templateName = "array-comprehension-filter";
 
-  return util.template(templateName, {
+  var result = util.template(templateName, {
     STATEMENT: node.body,
     FILTER:    node.filter,
     ARRAY:     block.right,
     KEY:       block.left
   });
+  result._aliasFunction = true;
+  return result;
 };
 
 var multiple = function (node, file) {
@@ -23,6 +25,7 @@ var multiple = function (node, file) {
   var container = util.template("array-comprehension-container", {
     KEY: uid
   });
+  container._aliasFunction = true;
 
   var block = container.callee.body;
   var body  = block.body;
@@ -47,7 +50,10 @@ var multiple = function (node, file) {
         var filter = util.template("if", {
           STATEMENT: node.filter
         });
+
+        // set if body
         filter.consequent.body = [child];
+
         child = filter;
       }
     }
@@ -56,7 +62,10 @@ var multiple = function (node, file) {
       ARRAY: self.right,
       KEY:   self.left
     }, true);
+
+    // set function body
     container2.expression.arguments[0].body.body = [child];
+
     return container2;
   };
 

lib/6to5/transformers/arrow-functions.js

@@ -1,58 +1,12 @@
-var traverse = require("../traverse");
 var util = require("../util");
-var b        = require("ast-types").builders;
 
-exports.ArrowFunctionExpression = function (node, parent, file) {
+exports.ArrowFunctionExpression = function (node) {
   util.ensureBlock(node);
 
+  node._aliasFunction = true;
+  node._aliasFunctionStopNonArrowFunctions = true;
   node.expression = false;
   node.type = "FunctionExpression";
 
-  if (traverse.hasType(node, "ThisExpression")) {
-    return util.template("function-bind-this", {
-      FUNCTION: node
-    });
-  } else {
   return node;
-  }
-};
-
-exports.FunctionDeclaration =
-exports.FunctionExpression = function (node, parent, file) {
-  var argumentsId;
-
-  var isArgumentIdentifier = function (node) {
-    return node.type === "Identifier" && node.name === "arguments";
-  };
-
-  var getId = function () {
-    return argumentsId = argumentsId || b.identifier(file.generateUid("arguments"));
-  };
-
-  // traverse the function and find all arrow functions so we can alias
-  // arguments if neccesary
-  traverse(node, function (node) {
-    if (node.type !== "ArrowFunctionExpression") return;
-
-    // traverse all child nodes of this arrow function and find a sole arguments
-    // identifier
-    traverse(node, function (node, parent) {
-      if (isArgumentIdentifier(node) && parent.type !== "MemberExpression") {
-        return getId();
-      } else if (node.type === "MemberExpression" && isArgumentIdentifier(node.object)) {
-        node.object = getId();
-      } else {
-        return;
-      }
-    }, traverse.FUNCTION_TYPES);
-
-    return false;
-  }, ["FunctionDeclaration", "FunctionExpression"]);
-
-  if (argumentsId) {
-    util.ensureBlock(node);
-    node.body.body.unshift(b.variableDeclaration("var", [
-      b.variableDeclarator(argumentsId, b.identifier("arguments"))
-    ]));
-  }
 };

lib/6to5/transformers/let-scoping.js

@@ -23,19 +23,7 @@ exports.VariableDeclaration = function (node, parent, file) {
     var id = ids[node.name];
     if (!id) return;
 
-    // we're a property key
+    if (util.isReferenced(node, parent)) return id;
-    if (parent.type === "Property" && parent.key === node) return;
-
-    var isMemberExpression = parent.type === "MemberExpression";
-
-    // we're in a member expression and we're the computed property so we're referenced
-    var isComputedProperty = isMemberExpression && parent.property === node && parent.computed;
-
-    // we're in a member expression and we're the object so we're referenced
-    var isObject = isMemberExpression && parent.object === node;
-
-    // we are referenced
-    if (!isMemberExpression || isComputedProperty || isObject) return id;
   };
 
   var replace = function (node, parent) {
@@ -55,7 +43,7 @@ exports.VariableDeclaration = function (node, parent, file) {
               b.returnStatement(node)
             ]
           )
-        ), letReferences)
+        ), letReferences);
       } else {
         return false;
       }

test/fixtures/syntax/array-comprehension/arguments/expected.js

@@ -1,6 +1,6 @@
 function add() {
   var _arguments = arguments;
-  return [1, 2, 3].map(function () {
+  return [1, 2, 3].map(function (i) {
     return i * _arguments[0];
   });
 }

test/fixtures/syntax/array-comprehension/this/expected.js

@@ -1,6 +1,6 @@
 function add() {
   var _this = this;
-  return [1, 2, 3].map(function () {
+  return [1, 2, 3].map(function (i) {
     return i * _this.multiplier;
   });
 }

test/fixtures/syntax/arrow-functions/arguments/actual.js

@@ -32,3 +32,14 @@ function five(obj) {
   return fn();
 }
 five({ arguments: ["foo"] });
+
+function six(obj) {
+  var fn = () => {
+    var fn2 = function () {
+      return arguments[0];
+    };
+    return fn2("foobar");
+  };
+  return fn();
+}
+six();

test/fixtures/syntax/arrow-functions/arguments/expected.js

@@ -43,3 +43,14 @@ function five(obj) {
   return fn();
 }
 five({ arguments: ["foo"] });
+
+function six(obj) {
+  var fn = function () {
+    var fn2 = function () {
+      return arguments[0];
+    };
+    return fn2("foobar");
+  };
+  return fn();
+}
+six();

test/fixtures/syntax/arrow-functions/this/expected.js

@@ -1,3 +1,4 @@
+var _this = this;
 var t = function (x) {
-  return this.x + x;
+  return _this.x + x;
-}.bind(this);
+};