In javascript, is it better to use two equal signs or three when comparing variables

Question

I have noticed quite a few people use three equals signs when comparing things in Javascript, but I was taught to only use two. Can anyone shed some light on why someone would use three or two, and why do they both work?

-Thanks :)

Another user has pointed out that the question has already been asked, sorry about that guys, going to look at the answers on that one.

Thanks, going to check that one out. – entropy May 19 '13 at 11:07 — entropy, May 19 '13 at 11:07

score 12 · Accepted Answer · edited May 19 '13 at 13:33

12

All the following evaluations will return true

With == JS will type-juggle.

1 == '1'
1 == 1
1 == true
0 != true
0 == false

With === JS will not type-juggle

1 !== '1'
1 === 1
1 !== true
0 !== false

edited May 19 '13 at 13:33

Qantas 94 Heavy

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answered May 19 '13 at 11:07

Jordan Doyle

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@Stano, please explain. I thought it was pretty obvious that `1 doesn't exactly equal '1'` (int to string) but `1 exactly equals 1` (int to int) on the first two examples of `===` – Jordan Doyle May 19 '13 at 11:13
Thanks @Stano, added into my answer. – Jordan Doyle May 19 '13 at 11:20

score 4 · Answer 2 · answered May 19 '13 at 11:09

The identity === operator is identical to the equality == operator except no type conversion is done therefore the types must be the same to be considered equal.

The == operator will compare for equality after doing any necessary type conversions.

The === operator will not do the conversion, so if two values are not the same type === will simply return false.

For me I generally always use === or !==, so as not to leave anything to chance.

score 3 · Answer 3 · answered May 19 '13 at 11:06

3

It depends on the use case. Triple equals is to check for identicality; in other words, not only equivalent, but the same type. Here's a good reference

answered May 19 '13 at 11:06

anomaaly

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score 1 · Answer 4 · answered May 19 '13 at 11:13

1

Triple equal will check the type of the variable also while double equal will only check for the match. If you want yo check the type of the variable, you need to use triple equals. Else you just need you use double equals.

answered May 19 '13 at 11:13

Anand

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In javascript, is it better to use two equal signs or three when comparing variables

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