add exponentiation operator

doc/differences.md

@@ -78,6 +78,7 @@ better suited if you'd like a full ES6 environment with polyfills and all.
 | Constants                    | ✓     | ✓       | ✓              |        |        |             |
 | Default parameters           | ✓     | ✓       | ✓              | ✓      | ✓      |             |
 | Destructuring                | ✓     | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Exponentiation operator      | ✓     | ✓       |                |        |        |             |
 | For-of                       | ✓     | ✓       | ✓              | ✓      | ✓      |             |
 | Generators                   | ✓     | ✓       |                | ✓      |        |             |
 | Generator comprehension      | ✓     | ✓       |                |        |        |             |

doc/features.md

@@ -130,6 +130,15 @@ var [a] = [];
 a === undefined;
 ```
 
+## Exponentiation operator ([experimental](usage.md#experimental)) ([spec](https://github.com/rwaldron/exponentiation-operator))
+
+```javascript
+var a = 2;
+a **= 2;
+
+var squared = 2 ** 2;
+```
+
 ## For-of
 
 ```javascript

doc/index.md

@@ -40,6 +40,7 @@ And it doesn't end here! To see all the ways you can use 6to5, check out the
  - [Constants](features.md#constants)
  - [Default parameters](features.md#default-parameters)
  - [Destructuring](features.md#destructuring)
+ - [Exponentiation operator](features.md#exponentiation-operator) ([experimental](usage.md#experimental))
  - [For-of](features.md#for-of)
  - [Generators](features.md#generators)
  - [Generator comprehension](features.md#generator-comprehension) ([experimental](usage.md#experimental))

lib/6to5/transformation/transform.js

@@ -39,6 +39,7 @@ _.each({
   computedPropertyNames:     require("./transformers/es6-computed-property-names"),
 
   objectSpread:              require("./transformers/es7-object-spread"),
+  exponentiationOperator:    require("./transformers/es7-exponentiation-operator"),
   spread:                    require("./transformers/es6-spread"),
   templateLiterals:          require("./transformers/es6-template-literals"),
   propertyMethodAssignment:  require("./transformers/es5-property-method-assignment"),

lib/6to5/transformation/transformers/es7-exponentiation-operator.js

@@ -0,0 +1,16 @@
+// https://github.com/rwaldron/exponentiation-operator
+
+var t = require("../../types");
+var pow = t.memberExpression(t.identifier("Math"), t.identifier("pow"));
+
+exports.AssignmentExpression = function (node) {
+  if (node.operator !== "**=") return;
+  node.operator = "=";
+  node.right = t.callExpression(pow, [node.left, node.right]);
+};
+
+exports.BinaryExpression = function (node) {
+  if (node.operator !== "**") return;
+
+  return t.callExpression(pow, [node.left, node.right]);
+};

package.json

@@ -47,7 +47,7 @@
     "chokidar": "0.11.1",
     "source-map-support": "0.2.8",
     "esutils": "1.1.6",
-    "acorn-6to5": "0.9.1-6",
+    "acorn-6to5": "0.9.1-7",
     "estraverse": "1.8.0",
     "private": "0.1.6"
   },

test/fixtures/transformation/es7-exponentian-operator/assignment/actual.js

@@ -0,0 +1 @@
+num **= 2;

test/fixtures/transformation/es7-exponentian-operator/assignment/expected.js

@@ -0,0 +1,3 @@
+"use strict";
+
+num = Math.pow(num, 2);

test/fixtures/transformation/es7-exponentian-operator/binary/actual.js

@@ -0,0 +1 @@
+2 ** 2;

test/fixtures/transformation/es7-exponentian-operator/binary/expected.js

@@ -0,0 +1,3 @@
+"use strict";
+
+Math.pow(2, 2);

test/fixtures/transformation/es7-exponentian-operator/options.json

@@ -0,0 +1,3 @@
+{
+  "experimental": true
+}