support array destructuring on iterables - fixes #194

doc/caveats.md

@@ -37,7 +37,7 @@ A polyfill is required for for-of functionality that implements `Symbol` and
 adds `prototype[Symbol.iterator]` behaviour to built-ins. Using the polyfills
 specified in [polyfill](polyfill.md) suffices.
 
-## Spread
+### Array destructuring / Spread
 
-An [ES6 polyfill](polyfill.md) is required in order for spread to work. More
+An [ES6 polyfill](polyfill.md) is required for spread and array destructuring.
-specifically a polyfill for `Array.from`.
+More specifically a polyfill for `Array.from`.

lib/6to5/templates/array-from.js

@@ -0,0 +1 @@
+Array.from(VALUE);

lib/6to5/transformation/transformers/destructuring.js

@@ -1,3 +1,4 @@
+var util = require("../../util");
 var t    = require("../../types");
 var _    = require("lodash");
 
@@ -11,45 +12,60 @@ var buildVariableAssign = function (kind, id, init) {
   }
 };
 
-var push = function (kind, nodes, elem, parentId) {
+var push = function (opts, nodes, elem, parentId) {
   if (t.isObjectPattern(elem)) {
-    pushObjectPattern(kind, nodes, elem, parentId);
+    pushObjectPattern(opts, nodes, elem, parentId);
   } else if (t.isArrayPattern(elem)) {
-    pushArrayPattern(kind, nodes, elem, parentId);
+    pushArrayPattern(opts, nodes, elem, parentId);
   } else if (t.isMemberExpression(elem)) {
     nodes.push(buildVariableAssign(false, elem, parentId));
   } else {
-    nodes.push(buildVariableAssign(kind, elem, parentId));
+    nodes.push(buildVariableAssign(opts.kind, elem, parentId));
   }
 };
 
-var pushObjectPattern = function (kind, nodes, pattern, parentId) {
+var pushObjectPattern = function (opts, nodes, pattern, parentId) {
   _.each(pattern.properties, function (prop) {
     var pattern2   = prop.value;
     var patternId2 = t.memberExpression(parentId, prop.key);
 
     if (t.isPattern(pattern2)) {
-      push(kind, nodes, pattern2, patternId2);
+      push(opts, nodes, pattern2, patternId2);
     } else {
-      nodes.push(buildVariableAssign(kind, pattern2, patternId2));
+      nodes.push(buildVariableAssign(opts.kind, pattern2, patternId2));
     }
   });
 };
 
-var pushArrayPattern = function (kind, nodes, pattern, parentId) {
+var pushArrayPattern = function (opts, nodes, pattern, parentId) {
+  var _parentId = t.identifier(opts.file.generateUid("ref", opts.scope));
+  nodes.push(t.variableDeclaration("var", [
+    t.variableDeclarator(_parentId, util.template("array-from", {
+      VALUE: parentId
+    }))
+  ]));
+  parentId = _parentId;
+
   _.each(pattern.elements, function (elem, i) {
     if (!elem) return;
 
     var newPatternId;
 
     if (t.isSpreadElement(elem)) {
-      newPatternId = t.callExpression(t.memberExpression(parentId, t.identifier("slice")), [t.literal(i)]);
+      newPatternId = util.template("array-from", {
+        VALUE: parentId
+      });
+
+      if (+i > 0) {
+        newPatternId = t.callExpression(t.memberExpression(newPatternId, t.identifier("slice")), [t.literal(i)]);
+      }
+
       elem = elem.argument;
     } else {
       newPatternId = t.memberExpression(parentId, t.literal(i), true);
     }
 
-    push(kind, nodes, elem, newPatternId);
+    push(opts, nodes, elem, newPatternId);
   });
 };
 
@@ -71,7 +87,7 @@ var pushPattern = function (opts) {
     parentId = key;
   }
 
-  push(kind, nodes, pattern, parentId);
+  push(opts, nodes, pattern, parentId);
 };
 
 exports.ForInStatement =
@@ -89,7 +105,11 @@ exports.ForOfStatement = function (node, parent, file, scope) {
 
   var nodes = [];
 
-  push(declar.kind, nodes, pattern, key);
+  push({
+    kind: declar.kind,
+    file: file,
+    scope: scope
+  }, nodes, pattern, key);
 
   t.ensureBlock(node);
 
@@ -141,7 +161,11 @@ exports.ExpressionStatement = function (node, parent, file, scope) {
     t.variableDeclarator(ref, expr.right)
   ]));
 
-  push(false, nodes, expr.left, ref);
+  push({
+    kind: false,
+    file: file,
+    scope: scope
+  }, nodes, expr.left, ref);
 
   return nodes;
 };

lib/6to5/transformation/transformers/spread.js

@@ -1,13 +1,13 @@
+var util = require("../../util");
 var t    = require("../../types");
 var _    = require("lodash");
 
 var getSpreadLiteral = function (spread) {
   var literal = spread.argument;
   if (!t.isArrayExpression(literal)) {
-    literal = t.callExpression(
+    literal = util.template("array-from", {
-      t.memberExpression(t.identifier("Array"), t.identifier("from")),
+      VALUE: literal
-      [literal]
+    });
-    );
   }
   return literal;
 };

test/fixtures/transformation/destructuring/array/expected.js

@@ -2,7 +2,13 @@
 
 var _ref = ["hello", [", ", "junk"], ["world"]];
 
-var a = _ref[0];
+var _ref2 = Array.from(_ref);
-var b = _ref[1][0];
+
-var c = _ref[2][0];
+var a = _ref2[0];
-var d = _ref[3];
+var _ref3 = Array.from(_ref2[1]);
+
+var b = _ref3[0];
+var _ref4 = Array.from(_ref2[2]);
+
+var c = _ref4[0];
+var d = _ref2[3];

test/fixtures/transformation/destructuring/assignment-statement/expected.js

@@ -2,5 +2,7 @@
 
 var _ref = f();
 
-a = _ref[0];
+var _ref2 = Array.from(_ref);
-b = _ref[1];
+
+a = _ref2[0];
+b = _ref2[1];

test/fixtures/transformation/destructuring/empty/expected.js

@@ -2,7 +2,13 @@
 
 var _ref = ["foo", "hello", [", ", "junk"], ["world"]];
 
-var a = _ref[1];
+var _ref2 = Array.from(_ref);
-var b = _ref[2][0];
+
-var c = _ref[3][0];
+var a = _ref2[1];
-var d = _ref[4];
+var _ref3 = Array.from(_ref2[2]);
+
+var b = _ref3[0];
+var _ref4 = Array.from(_ref2[3]);
+
+var c = _ref4[0];
+var d = _ref2[4];

test/fixtures/transformation/destructuring/for-in/expected.js

@@ -1,7 +1,9 @@
 "use strict";
 
 for (var _ref in obj) {
-  var name = _ref[0];
+  var _ref2 = Array.from(_ref);
-  var value = _ref[1];
+
+  var name = _ref2[0];
+  var value = _ref2[1];
   print("Name: " + name + ", Value: " + value);
 }

test/fixtures/transformation/destructuring/for-of/expected.js

@@ -2,7 +2,9 @@
 
 for (var _iterator = this.test.expectation.registers[Symbol.iterator](), _step; !(_step = _iterator.next()).done;) {
   var _ref = _step.value;
-  var name = _ref[0];
+  var _ref2 = Array.from(_ref);
-  var before = _ref[1];
+
-  var after = _ref[2];
+  var name = _ref2[0];
+  var before = _ref2[1];
+  var after = _ref2[2];
 }

test/fixtures/transformation/destructuring/member-expression/expected.js

@@ -2,5 +2,7 @@
 
 var _ref = [1, 2];
 
-this.foo = _ref[0];
+var _ref2 = Array.from(_ref);
-this.bar = _ref[1];
+
+this.foo = _ref2[0];
+this.bar = _ref2[1];

test/fixtures/transformation/destructuring/mixed/expected.js

@@ -1,6 +1,10 @@
 "use strict";
 
-var x1 = rect.topLeft[0];
+var _ref = Array.from(rect.topLeft);
-var y1 = rect.topLeft[1];
+
-var x2 = rect.bottomRight[0];
+var x1 = _ref[0];
-var y2 = rect.bottomRight[1];
+var y1 = _ref[1];
+var _ref2 = Array.from(rect.bottomRight);
+
+var x2 = _ref2[0];
+var y2 = _ref2[1];

test/fixtures/transformation/destructuring/parameters/expected.js

@@ -15,13 +15,17 @@ function unpackObject(_ref2) {
 
 console.log(unpackObject({ title: "title", author: "author" }));
 
-var unpackArray = function (_ref3, _ref4) {
+var unpackArray = function (_ref3, _ref5) {
-  var a = _ref3[0];
+  var _ref4 = Array.from(_ref3);
-  var b = _ref3[1];
+
-  var c = _ref3[2];
+  var a = _ref4[0];
-  var x = _ref4[0];
+  var b = _ref4[1];
-  var y = _ref4[1];
+  var c = _ref4[2];
-  var z = _ref4[2];
+  var _ref6 = Array.from(_ref5);
+
+  var x = _ref6[0];
+  var y = _ref6[1];
+  var z = _ref6[2];
   return a + b + c;
 };
 

test/fixtures/transformation/destructuring/spread-generator/exec.js

@@ -0,0 +1,7 @@
+function* f() {
+  for (var i = 0; i < 3; i++) {
+    yield i;
+  }
+}
+var [...xs] = f();
+assert.deepEqual(xs, [0, 1, 2]);

test/fixtures/transformation/destructuring/spread/expected.js

@@ -1,9 +1,11 @@
 "use strict";
 
 var isSorted = function (_ref) {
-  var x = _ref[0];
+  var _ref2 = Array.from(_ref);
-  var y = _ref[1];
+
-  var wow = _ref.slice(2);
+  var x = _ref2[0];
+  var y = _ref2[1];
+  var wow = Array.from(_ref2).slice(2);
 
   if (!zs.length) return true;
   if (y > x) return isSorted(zs);