enforcing +0 !== -0

index.js

@@ -9,8 +9,12 @@ var Object_keys = typeof Object.keys === 'function'
 ;
 
 var deepEqual = module.exports = function (actual, expected) {
+  // enforce Object.is +0 !== -0
+  if (actual === 0 && expected === 0) {
+    return areZerosEqual(actual, expected);
+
   // 7.1. All identical values are equivalent, as determined by ===.
-  if (actual === expected) {
+  } else if (actual === expected) {
     return true;
 
   } else if (actual instanceof Date && expected instanceof Date) {
@@ -33,7 +37,7 @@ var deepEqual = module.exports = function (actual, expected) {
   } else {
     return objEquiv(actual, expected);
   }
-}
+};
 
 function isUndefinedOrNull(value) {
   return value === null || value === undefined;
@@ -48,6 +52,11 @@ function isNumberNaN(value) {
   return typeof value == 'number' && value !== value;
 }
 
+function areZerosEqual(zeroA, zeroB) {
+  // (1 / +0|0) -> Infinity, but (1 / -0) -> -Infinity and (Infinity !== -Infinity)
+  return (1 / zeroA) === (1 / zeroB);
+}
+
 function objEquiv(a, b) {
   if (isUndefinedOrNull(a) || isUndefinedOrNull(b))
     return false;

test/neg-vs-pos-0.js

@@ -0,0 +1,15 @@
+var test = require('tape');
+var equal = require('../');
+
+test('0 values', function (t) {
+    t.ok(equal( 0,  0), ' 0 ===  0');
+    t.ok(equal( 0, +0), ' 0 === +0');
+    t.ok(equal(+0, +0), '+0 === +0');
+    t.ok(equal(-0, -0), '-0 === -0');
+
+    t.notOk(equal(-0,  0), '-0 !==  0');
+    t.notOk(equal(-0, +0), '-0 !== +0');
+
+    t.end();
+});
+