add support for ES7 exponentiation operator

README.md

@@ -5,4 +5,5 @@ Deviates from [acorn](https://github.com/marijnh/acorn) in the following ways:
  * JSX support via [acorn-jsx](https://github.com/RReverser/acorn-jsx)
  * [ES7 Abstract references](https://github.com/zenparsing/es-abstract-refs)
  * [ES7 Async/await](https://github.com/lukehoban/ecmascript-asyncawait)
- * [ES7 Object Rest/Spread](https://github.com/sebmarkbage/ecmascript-rest-spread)
+ * [ES7 Exponentiation operator](https://github.com/rwaldron/exponentiation-operator)
+ * [ES7 Object rest/spread](https://github.com/sebmarkbage/ecmascript-rest-spread)

acorn.js

@@ -462,6 +462,7 @@
 
   // '*' may be multiply or have special meaning in ES6
   var _star = {binop: 10, beforeExpr: true};
+  var _exponent = {binop: 10, beforeExpr: true};
 
   // '<', '>' may be relational or have special meaning in JSX
   var _lt = {binop: 7, beforeExpr: true}, _gt = {binop: 7, beforeExpr: true};
@@ -475,7 +476,7 @@
                       name: _name, eof: _eof, num: _num, regexp: _regexp, string: _string,
                       arrow: _arrow, bquote: _bquote, dollarBraceL: _dollarBraceL, star: _star,
                       assign: _assign, xjsName: _xjsName, xjsText: _xjsText,
-                      doubleColon: _doubleColon};
+                      doubleColon: _doubleColon, exponent: _exponent};
   for (var kw in keywordTypes) exports.tokTypes["_" + kw] = keywordTypes[kw];
 
   // This is a trick taken from Esprima. It turns out that, on
@@ -751,10 +752,29 @@
     return finishOp(_slash, 1);
   }
 
-  function readToken_mult_modulo(code) { // '%*'
+  function readToken_modulo() { // '%'
     var next = input.charCodeAt(tokPos + 1);
     if (next === 61) return finishOp(_assign, 2);
-    return finishOp(code === 42 ? _star : _modulo, 1);
+    return finishOp(_modulo, 1);
+  }
+
+  function readToken_mult() { // '*'
+    var type = _star;
+    var width = 1;
+    var next = input.charCodeAt(tokPos + 1);
+
+    if (options.ecmaVersion >= 7 && next === 42) { // '*'
+      width++;
+      next = input.charCodeAt(tokPos + 2);
+      type = _exponent;
+    }
+
+    if (next === 61) { // '='
+      width++;
+      type = _assign;
+    }
+    
+    return finishOp(type, width);
   }
 
   function readToken_pipe_amp(code) { // '|&'
@@ -907,8 +927,11 @@
     case 47: // '/'
       return readToken_slash();
 
-    case 37: case 42: // '%*'
-      return readToken_mult_modulo(code);
+    case 37: // '%'
+      return readToken_modulo();
+
+    case 42: // '*'
+      return readToken_mult();
 
     case 124: case 38: // '|&'
       return readToken_pipe_amp(code);

package.json

@@ -2,7 +2,7 @@
   "name": "acorn-6to5",
   "description": "Acorn fork used by 6to5",
   "main": "acorn.js",
-  "version": "0.9.1-6",
+  "version": "0.9.1-7",
   "maintainers": [
     {
       "name": "Marijn Haverbeke",

test/tests-6to5.js

@@ -4,6 +4,82 @@ if (typeof exports != "undefined") {
   var testAssert = require("./driver.js").testAssert;
 }
 
+// ES7: Exponentiation Operator
+
+test('a **= 2;', {
+  type: "Program",
+  start: 0,
+  end: 8,
+  body: [{
+    type: "ExpressionStatement",
+    start: 0,
+    end: 8,
+    expression: {
+      type: "AssignmentExpression",
+      start: 0,
+      end: 7,
+      operator: "**=",
+      left: {
+        type: "Identifier",
+        start: 0,
+        end: 1,
+        name: "a"
+      },
+      right: {
+        type: "Literal",
+        start: 6,
+        end: 7,
+        value: 2
+      }
+    }
+  }]
+}, {
+  ecmaVersion: 7
+});
+
+test('var squared = 2 ** 2;', {
+  type: "Program",
+  start: 0,
+  end: 21,
+  body: [{
+    type: "VariableDeclaration",
+    start: 0,
+    end: 21,
+    declarations: [{
+      type: "VariableDeclarator",
+      start: 4,
+      end: 20,
+      id: {
+        type: "Identifier",
+        start: 4,
+        end: 11,
+        name: "squared"
+      },
+      init: {
+        type: "BinaryExpression",
+        start: 14,
+        end: 20,
+        left: {
+          type: "Literal",
+          start: 14,
+          end: 15,
+          value: 2
+        },
+        operator: "**",
+        right: {
+          type: "Literal",
+          start: 19,
+          end: 20,
+          value: 2
+        }
+      }
+    }],
+    kind: "var"
+  }]
+}, {
+  ecmaVersion: 7
+});
+
 // ES7: Object Rest/Spread
 
 test('let {...x} = z', {