Meaning of === operator in javascript

Question

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JavaScript === vs == : Does it matter which “equal” operator I use?

Example as:

if (c === 0){
   //
}

What is the meaning of === here in above ex?

http://stackoverflow.com/questions/359494/javascript-vs-does-it-matter-which-equal-operator-i-use — Hadas, Feb 07 '12 at 07:53
http://stackoverflow.com/questions/359494/javascript-vs-does-it-matter-which-equal-operator-i-use — JKing, Feb 07 '12 at 07:54

score 2 · Answer 1 · answered Feb 07 '12 at 07:53

2

It checks that c is equal to the number 0. === is the strict equality operator. It does not attempt to type coerce the operands.

For example:

0 == false; //true (false coerces to 0)
0 === false; //false (no type coercion)

answered Feb 07 '12 at 07:53

James Allardice

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in other words, it check the values *and* the type – Joseph Feb 07 '12 at 07:55
@Joseph - Yeah that might have been a simpler way to put it :) – James Allardice Feb 07 '12 at 07:56
and to clarify a little more, "0" === "0" is true – Steve Feb 07 '12 at 07:57
@Steve - I think that goes without saying... they are both strings. – James Allardice Feb 07 '12 at 07:58
I know, but it was just to give an example that had a true result. If the person is asking the question, why not give a complete answer? – Steve Feb 07 '12 at 08:37

score 2 · Answer 2 · answered Feb 07 '12 at 08:00

2

a == b means that a equals b

a === b means that a equals b and their types are the same

answered Feb 07 '12 at 08:00

score 1 · Answer 3 · answered Feb 07 '12 at 07:54

This is the strict equal operator and only returns a Boolean true if both the operands are equal and of the same type. Assume these:

a = 2
b = 4

These next examples return true:

a === 2 
b === 4

There is also a reverse of this operator: !== This is the strict not equal operator and only returns a value of true if both the operands are not equal and/or not of the same type. The following examples return a Boolean true:

a !== b 
a !== "2" 
4 !== '4'

All quoted from here: http://www.devguru.com/technologies/ecmascript/quickref/comparison_operators.html

score 0 · Answer 4 · answered Feb 07 '12 at 07:55

Here is a sample

<script type="text/javascript">
        var y = 0;
        if(y == "0"){
            document.write("== '0' True <br/>");
        }
        else{
            document.write("== '0' False <br/>");
        }

        if(y == 0){
            document.write("== 0 Number is True <br/>");
        }
        else{
            document.write("== 0 Number False <br/>");
        }

        if( y === 0){
            document.write("=== 0 Number is True <br/>");
        }
        else{
            document.write("=== 0 Number is False <br/>");
        }

        if(y === "0"){
            document.write("=== 0 is True <br/>");
        }
        else{
            document.write("=== 0 is False<br/>");
        }
    </script>

If the right value is 0 , you will get

== '0' True
== 0 Number is True
=== 0 Number  is True
=== 0 is False

score 0 · Answer 5 · answered Feb 07 '12 at 07:57

0

The == operator only checks for equivalence of two values while the === operator goes an additional step and also asserts that the types of the two values are the same.

2 == "2" // true

While:

2 === "2" // false

answered Feb 07 '12 at 07:57

Ates Goral

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Meaning of === operator in javascript

5 Answers5