From 23cf77746da1554a3b78e3e6c949289c7b74c247 Mon Sep 17 00:00:00 2001
From: Sebastian McKenzie <sebmck@gmail.com>
Date: Fri, 31 Jul 2015 01:37:50 +0100
Subject: [PATCH] optimise common typeof cases in es6.spec.symbols transformer

---
 .../src/transformation/transformers/es6/spec.symbols.js     | 6 ++++++
 packages/babel/src/types/index.js                           | 3 ++-
 .../transformation/es6.spec.symbols/typeof/actual.js        | 2 ++
 .../fixtures/transformation/es6.spec.symbols/typeof/exec.js | 1 +
 .../transformation/es6.spec.symbols/typeof/expected.js      | 2 ++
 5 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/packages/babel/src/transformation/transformers/es6/spec.symbols.js b/packages/babel/src/transformation/transformers/es6/spec.symbols.js
index 455fc4ac7e..80eaf22788 100644
--- a/packages/babel/src/transformation/transformers/es6/spec.symbols.js
+++ b/packages/babel/src/transformation/transformers/es6/spec.symbols.js
@@ -17,6 +17,12 @@ export var visitor = {
   UnaryExpression(node, parent, scope, file) {
     if (node._ignoreSpecSymbols) return;
 
+    if (this.parentPath.isBinaryExpression() && t.EQUALITY_BINARY_OPERATORS.indexOf(parent.operator) >= 0) {
+      // optimise `typeof foo === "string"` since we can determine that they'll never need to handle symbols
+      var opposite = this.getOpposite();
+      if (opposite.isLiteral() && opposite.node.value !== "symbol" && opposite.node.value !== "object") return;
+    }
+
     if (node.operator === "typeof") {
       var call = t.callExpression(file.addHelper("typeof"), [node.argument]);
       if (this.get("argument").isIdentifier()) {
diff --git a/packages/babel/src/types/index.js b/packages/babel/src/types/index.js
index dce4e78b1a..8975faea2f 100644
--- a/packages/babel/src/types/index.js
+++ b/packages/babel/src/types/index.js
@@ -39,7 +39,8 @@ export const INHERIT_KEYS = {
 };
 
 export const BOOLEAN_NUMBER_BINARY_OPERATORS = [">", "<", ">=", "<="];
-export const COMPARISON_BINARY_OPERATORS     = ["==", "===", "!=", "!==", "in", "instanceof"];
+export const EQUALITY_BINARY_OPERATORS       = ["==", "===", "!=", "!=="];
+export const COMPARISON_BINARY_OPERATORS     = EQUALITY_BINARY_OPERATORS.concat(["in", "instanceof"]);
 export const BOOLEAN_BINARY_OPERATORS        = [].concat(COMPARISON_BINARY_OPERATORS, BOOLEAN_NUMBER_BINARY_OPERATORS);
 export const NUMBER_BINARY_OPERATORS         = ["-", "/", "*", "**", "&", "|", ">>", ">>>", "<<", "^"];
 
diff --git a/packages/babel/test/fixtures/transformation/es6.spec.symbols/typeof/actual.js b/packages/babel/test/fixtures/transformation/es6.spec.symbols/typeof/actual.js
index d31f30ca86..872484bd9c 100644
--- a/packages/babel/test/fixtures/transformation/es6.spec.symbols/typeof/actual.js
+++ b/packages/babel/test/fixtures/transformation/es6.spec.symbols/typeof/actual.js
@@ -1,3 +1,5 @@
 var s = Symbol("s");
+assert.ok(typeof s === "symbol");
 assert.equal(typeof s, "symbol");
 assert.equal(typeof typeof s.foo, "symbol");
+typeof s === "string";
diff --git a/packages/babel/test/fixtures/transformation/es6.spec.symbols/typeof/exec.js b/packages/babel/test/fixtures/transformation/es6.spec.symbols/typeof/exec.js
index 20422ebc64..0c53760815 100644
--- a/packages/babel/test/fixtures/transformation/es6.spec.symbols/typeof/exec.js
+++ b/packages/babel/test/fixtures/transformation/es6.spec.symbols/typeof/exec.js
@@ -1,2 +1,3 @@
 var s = Symbol("s");
 assert.equal(typeof s, "symbol");
+assert.ok(typeof s === "symbol");
diff --git a/packages/babel/test/fixtures/transformation/es6.spec.symbols/typeof/expected.js b/packages/babel/test/fixtures/transformation/es6.spec.symbols/typeof/expected.js
index 80d011bc00..fc73784fe4 100644
--- a/packages/babel/test/fixtures/transformation/es6.spec.symbols/typeof/expected.js
+++ b/packages/babel/test/fixtures/transformation/es6.spec.symbols/typeof/expected.js
@@ -1,5 +1,7 @@
 "use strict";
 
 var s = Symbol("s");
+assert.ok((typeof s === "undefined" ? "undefined" : babelHelpers._typeof(s)) === "symbol");
 assert.equal(typeof s === "undefined" ? "undefined" : babelHelpers._typeof(s), "symbol");
 assert.equal(babelHelpers._typeof(babelHelpers._typeof(s.foo)), "symbol");
+typeof s === "string";