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Difference between == and === in JavaScript
Javascript === vs == : Does it matter which “equal” operator I use?
What's the difference between == and ===? Also between !== and !==?
There are lots of answers to this question on Stackoverflow already.
Short:
== only compares values
=== compares values + type
var check1 = '10',
check2 = 10;
check1 == check2 // true
check1 === check2 // false
"==" means equals, whereas "===" means identically equal.
In short, "==" will try and coerce/convert the types of values when doing a comparison, so "2"==2, whereas "===" will not.
Related
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Difference between == and === in JavaScript [duplicate]
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Closed 6 years ago.
I am using java script to compare values
if (cellValue == "true" || cellValue == true)
Instead of doing this can i use the ===operator in java script ?
The difference between == and === is that the first one (double equals) does type coercion, which can lead to goofy results:
0 == false
true
0 === false
false
It is usually recommended to use === as that will provide more predictable results and evaluate the true types of the values you're comparing.
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JavaScript === vs == : Does it matter which “equal” operator I use?
Javascript operator !==
What's the difference between != and !==?
Can you give me an example where using != gives another result than using !==?
alert(1 != true);
alert(1 !== true);
The first one is false, the second true.
!= accept 1 as equals of true, null as equals of false and some others (because the values are automatically casted when being compared).
!== accept only "real" equalities (i.e. compares both the value and the type).
Example
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JavaScript === vs == : Does it matter which “equal” operator I use?
The 3 different equals
I'm trying to understand what is happening here:
data.toPage = $('div#someID');
if ( typeof data.toPage === "string" ) {
// sth
console.log("hello");
}
So I'm checking for a string am I not? I'm curious because my console "helloes".
Thanks for some input!
==
This is the equal operator and returns a boolean true if both the operands are equal. JavaScript will attempt to convert different data types to the same type in order to make the comparison. Assuming 'a' to be 2 and 'b' to be 4, the following examples will return a value of true:
a == 2
a == "2"
2 == '2'
===
This is the strict equal operator and only returns a Boolean true if both the operands are equal and of the same type. These next examples return true:
a === 2
b === 4
The triple equals sign === compares both value and type, whereas the double == only compares value
for example "1" and 1 have the same value (so to speak) but are of different types. Therefore the following will occur:
"1" == 1 //true
"1" === 1 //false
This is a great read for some useful javascript knowledge, which includes the triple equals amongst other good-to-know stuff
The === comparison operator means that the two values won't have their types modified before the comparison is made, so they need to be of the same type as well as representing the same value for it to return true.
'1' == 1 // true
'1' === 1 // false
This question already has answers here:
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Javascript === vs == : Does it matter which “equal” operator I use?
Hi,
This is my tiny code:
var domains_before_update = storage.getItem('domain_list_original');
if(domains_before_update==null || domains_before_update=="" )
{
gBrowser.selectedTab = gBrowser.addTab("chrome://filter/content/block_and_redirect_list.html");
}
Is that correct or should I be using === instead of == ?
Thanks!
=== checks the strict equals (without coercion) that you're used to , where == checks the value [after built-in coercion] equality
but as the other answer(s) noted, strict equality does not work when checking for null, use !variable
same as this post: Difference between == and === in JavaScript
edit: clarified some of the wording thanks to the helpful comments!
In this case, it doesn't matter - and in all cases where it doesn't matter, you should use strict equality or identity, e.g. ===.
Neither.
Use:
if(!domains_before_update)
{
}
For comparisons with null, === is required.
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Javascript === vs == : Does it matter which “equal” operator I use?
Why do I see lots of javascript code lately with expressions that look like this:
if(val === "something")
Why "===" instead of just "=="? What's the difference? When should I use one or the other?
The === does not allow type coercion, so something like this would return false:
if (2 === '2') // false
The "normal" javascript == operator does allow type coercion, and so this would return true:
if (2 == '2') // true
var a = 3;
var b = "3";
if (a == b) {
// this is true.
}
if (a === b) {
// this is false.
}
=== is typically referred to as the identity operator. Values being compared must be of the same type and value to be considered equal. == is typically referred to as the equality operator and performs type coercion to check equality.
An example
1 == '1' // returns true even though one is a number, the other a string
1 === '1' // returns false. different datatypes
Doug Crockford touches briefly on this in JavaScript the Good Parts google tech talk video. Worth spending an hour to watch.
Checks that the type as well as the values match. This is important since (0 == false) is true but (0 === false) is not true.