Object comparisons in JavaScript

Question

I would like to understand the weird behaviour of JavaScript identity and equality operator as given below.

var a = {};
var b = {};
a === b; //false
a == b;  //false

var c = '';
var d = '';
c === d; //true
c == d;  //true

All four variables a ,b ,c and d are objects. But when comparing them, first case yields false whereas second one true.

I studied comparison from the following source: https://msdn.microsoft.com/en-us/library/d53a7bd4(v=vs.94).aspx

According to the above article, except number and boolean everything is compared by reference instead of value. So how the first case returns false and second one true.

`So how the first case returns true and second one false.` other way around, first is false, second is true — Jaromanda X, Aug 24 '16 at 13:20
Strings are primitives. Welcome to the beautiful world of JS. — Tamas Hegedus, Aug 24 '16 at 13:20
Possible duplicate of [Is String a Primitive type or Object in Javascript?](http://stackoverflow.com/questions/7675127/is-string-a-primitive-type-or-object-in-javascript) — Tamas Hegedus, Aug 24 '16 at 13:21
try `var c = new String(''), d = new String('');` then see how you go — Jaromanda X, Aug 24 '16 at 13:21
The article you linked to in the question says explicitly that strings are compared by value. — nnnnnn, Aug 24 '16 at 13:22
Possible duplicate of [Object comparison in JavaScript](http://stackoverflow.com/questions/1068834/object-comparison-in-javascript) — random_user_name, Aug 24 '16 at 13:22

score 1 · Accepted Answer · answered Aug 24 '16 at 13:22

c and d in your example are strings, which are primitive types in JavaScript and compared by value.

For this reason, c == d returns true.

The article is talking about string objects created usng the new String('foo') constructor, which actually creates objects. In this case, the references are compared, returning false.

console.log(new String('foo') == new String('foo')) // false
console.log('foo' == 'foo')                         // true

Thilo · Answer 2 · 2016-08-24T13:26:57.267

A (primitive) string is a value type (like Number). As such === compares its value (equality).

Objects are reference types, and for them === compares identity.

Strings are a bit crazy, as there are both primitive strings and String objects (created with new String("foo")).

== works the same way as === except that it does type conversions to "make things equal if possible". For reference types this is the same as ===, except that it also equates primitive strings and String objects.

 "abc" == new String("abc");
 "abc" !== new String("abc");

Object comparisons in JavaScript

2 Answers2