Merge pull request eslint#713 from btmills/eqeqeq-null

Relax eqeqeq null check (fixes eslint#669)
btmills · Mar 26, 2014 · 44460ff · 44460ff
2 parents e1136cb + 19cc7e2
commit 44460ff
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Showing 3 changed files with 15 additions and 6 deletions.
diff --git a/docs/rules/eqeqeq.md b/docs/rules/eqeqeq.md
@@ -28,8 +28,7 @@ if (obj.getStuff() != undefined) { ... }
 
 - `"smart"`
 
-This option will enforce `===` and `!==` in your code unless you're comparing between literals
-or you're doing a `typeof` comparison. For those types of comparisons using strict equality is unnecessary.
+This option will enforce `===` and `!==` in your code unless you're comparing between literals or you're doing a `typeof` comparison. For those types of comparisons using strict equality is unnecessary. It also permits comparing to `null` to check for `null` or `undefined` in a single expression.
 
 The following patterns are considered okay and do not cause warnings:
 
@@ -38,6 +37,7 @@ typeof foo == 'undefined'
 'hello' != 'world'
 0 == 0
 true == true
+foo == null
 ```
 
 The following patterns are considered warnings with "smart:

diff --git a/lib/rules/eqeqeq.js b/lib/rules/eqeqeq.js
@@ -18,14 +18,21 @@ module.exports = function(context) {
     }
 
     function bothAreSameTypeLiterals(node) {
-        return node.left.type === "Literal" && node.right.type === "Literal" && typeof node.left.value === typeof node.right.value;
+        return node.left.type === "Literal" && node.right.type === "Literal" &&
+                typeof node.left.value === typeof node.right.value;
+    }
+
+    function isNullCheck(node) {
+        return (node.right.type === "Literal" && node.right.value === null) ||
+                (node.left.type === "Literal" && node.left.value === null);
     }
 
     return {
         "BinaryExpression": function(node) {
             var operator = node.operator;
 
-            if (context.options[0] === "smart" && (isTypeOf(node) || bothAreSameTypeLiterals(node))) {
+            if (context.options[0] === "smart" && (isTypeOf(node) ||
+                    bothAreSameTypeLiterals(node)) || isNullCheck(node)) {
                 return;
             }
 
@@ -36,4 +43,4 @@ module.exports = function(context) {
             }
         }
     };
-};
+};
diff --git a/tests/lib/rules/eqeqeq.js b/tests/lib/rules/eqeqeq.js
@@ -21,7 +21,9 @@ eslintTester.addRuleTest("lib/rules/eqeqeq", {
         { code: "'string' != typeof a", args: [1, "smart"] },
         { code: "'hello' != 'world'", args: [1, "smart"] },
         { code: "2 == 3", args: [1, "smart"] },
-        { code: "true == true", args: [1, "smart"] }
+        { code: "true == true", args: [1, "smart"] },
+        { code: "null == a", args: [1, "smart"] },
+        { code: "a == null", args: [1, "smart"] }
     ],
     invalid: [
         { code: "a == b", errors: [{ message: "Expected '===' and instead saw '=='.", type: "BinaryExpression"}] },