Values comparison

Question

[4] === 4 // is: false
[4] == 4 // is: true

'0' == 0 // is: true
'0' === 0 // is: false

Can anyone give the exact reason for this?Also what exactly does strict equality operator do or need for comparision?I learned that type and value should be same for strict(===) operator.Is this what strict equality operator checks .If yes,than how equl to operator works?

Derek 朕會功夫 · Accepted Answer · 2013-04-13T06:21:56.767

4

== Compare values
=== Compare values and type

For example

[4] //turns into "4" when comparing
"4" == 4 //They are the same

"4" === 4 //The values are the same, but not the type

Reference: http://es5.github.io/#x11.9.4

https://i.stack.imgur.com/q13LO.png

edited Apr 13 '13 at 06:21

answered Apr 13 '13 at 05:36

Derek 朕會功夫

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how can "4" be equal to 4 .One is string and one is number. – Maizere Pathak.Nepal Apr 13 '13 at 05:38
@Maizere - `==` [does not care its type](http://es5.github.io/#x11.9.3). – Derek 朕會功夫 Apr 13 '13 at 05:39
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@Maizere Welcome to javascript – painotpi Apr 13 '13 at 05:40
@Derek 朕會功夫 did u mean it only takes care of values – Maizere Pathak.Nepal Apr 13 '13 at 05:40
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@Maizere - Actually, it will turn your String into a Number when comparing a String to a Number as it stated in [the spec](http://es5.github.io/#x11.9.3). So the type is not a factor when using `==`. – Derek 朕會功夫 Apr 13 '13 at 05:41
@badZoke ur username should be goodZoke – Maizere Pathak.Nepal Apr 13 '13 at 05:42
@Maizere - More mind-blown: `[4] == [4] //false` – Derek 朕會功夫 Apr 13 '13 at 05:47
@Derek 朕會功夫 oh no.How can this be false again?i m having a severe pain in my head now – Maizere Pathak.Nepal Apr 13 '13 at 05:49
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@Maizere In that case, the comparison is of references. Since each `[4]` is a `new Array()`, they aren't the *same*; only *similar*, which `==` doesn't check for. – Jonathan Lonowski Apr 13 '13 at 05:52
@ Jonathan Lonowski To quote Douglas Crockford's excellent JavaScript: The Good Parts, evil twins(==) do the right thing when the operands are of the same type, but if they are of different types, they attempt to coerce the values.this means [4]==[4] should be equal becoz both are of same type – Maizere Pathak.Nepal Apr 13 '13 at 05:55
@ Derek 朕會功夫 To quote Douglas Crockford's excellent JavaScript: The Good Parts, evil twins(==) do the right thing when the operands are of the same type, but if they are of different types, they attempt to coerce the values.this means [4]==[4] should be equal becoz both are of same type – Maizere Pathak.Nepal Apr 13 '13 at 05:56
@Maizere - According to the spec, when comparing an Array to another Array, unless they have the same reference, it will always return `false`. – Derek 朕會功夫 Apr 13 '13 at 05:56
@Derek朕會功夫 Do this apply only in case of an array or it applies for variables too? – Maizere Pathak.Nepal Apr 13 '13 at 05:58
@Maizere - If you are comparing variables referring to the same Array, it would return `true`: `var a=b=[4]; a === b //true` – Derek 朕會功夫 Apr 13 '13 at 06:01
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@Maizere It applies to any 2 `Object`s (non-primitives) -- `new String()` vs. `""`; `new Number()` vs. `0`; as well as `Object`, `Array`, `RegExp`, `Function`, etc. In comparing 2 `Object`s, you're comparing references, so they must be references to the exact same `Object` to be equal. So, `var a = [], b = a; a == b;` vs. `[] == [];` – Jonathan Lonowski Apr 13 '13 at 06:02
@ Derek 朕會功夫 i mean are this false like say:x=10;y=10 (x==y)? – Maizere Pathak.Nepal Apr 13 '13 at 06:03
@Maizere - It will return `true`. Why would it false anyway? – Derek 朕會功夫 Apr 13 '13 at 06:05
@ Derek 朕會功夫 false == 'false' //false why?since false should be coerced to string and the output should be true – Maizere Pathak.Nepal Apr 13 '13 at 06:13
@Maizere - No, [the spec](http://es5.github.io/#x11.9.4) says if the left hand side is Boolean, then it will be changed into a Number. `false == 0 //true` ([whisper]JavaScript sucks![whisper]) – Derek 朕會功夫 Apr 13 '13 at 06:17

score 1 · Answer 2 · answered Apr 13 '13 at 05:37

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The === operator also compares the type of the object.

So, in [4] === 4

[4] is an array, but 4 is a number, so that evaluates to false.

And in '0' === 0

'0' is a string, but 0 is a number, so that evaluates to false.

answered Apr 13 '13 at 05:37

painotpi

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what about equal(==) to operator – Maizere Pathak.Nepal Apr 13 '13 at 05:39
the `==` compares only the value. Not the type. – painotpi Apr 13 '13 at 05:39

score 0 · Answer 3 · answered Apr 13 '13 at 05:36

The === operator compares both type and value, making it a stricter check. The == operator performs a less strict value based checked. It will in some cases consider values of different types "equal" Such examples are 0 vs '' or 0 vs "0"

The == operator will see 0 and '' as equal whereas the === operator will not treat them as equal since they are of different types.

Values comparison

3 Answers3

For example