use Array.from on single block array comprehensions - closes #199

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

@@ -2,16 +2,21 @@ var util = require("../../util");
 var t    = require("../../types");
 var _    = require("lodash");
 
-var singleArrayExpression = function (node) {
+var single = function (node) {
   var block = node.blocks[0];
 
   var templateName = "array-expression-comprehension-map";
   if (node.filter) templateName = "array-expression-comprehension-filter";
 
+  var right = block.right;
+  if (!t.isArrayExpression(right)) {
+    right = util.template("array-from", { VALUE: right });
+  }
+
   var result = util.template(templateName, {
     STATEMENT: node.body,
     FILTER:    node.filter,
-    ARRAY:     block.right,
+    ARRAY:     right,
     KEY:       block.left
   });
 
@@ -73,8 +78,8 @@ exports._build = function (node, buildBody) {
 exports.ComprehensionExpression = function (node, parent, file) {
   if (node.generator) return;
 
-  if (node.blocks.length === 1 && t.isArrayExpression(node.blocks[0].right)) {
-    return singleArrayExpression(node);
+  if (node.blocks.length === 1) {
+    return single(node);
   } else {
     return multiple(node, file);
   }

test/fixtures/transformation/array-comprehension/single-if/actual.js

@@ -0,0 +1 @@
+var arr = [for (i of nums) if (i > 1) i * i];

test/fixtures/transformation/array-comprehension/single-if/expected.js

@@ -0,0 +1,7 @@
+"use strict";
+
+var arr = Array.from(nums).filter(function (i) {
+  return i > 1;
+}).map(function (i) {
+  return i * i;
+});

test/fixtures/transformation/array-comprehension/single/actual.js

@@ -0,0 +1 @@
+var arr = [for (i of nums) i * i];

test/fixtures/transformation/array-comprehension/single/expected.js

@@ -0,0 +1,5 @@
+"use strict";
+
+var arr = Array.from(nums).map(function (i) {
+  return i * i;
+});