Difference between !== and !=

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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 !==?

http://stackoverflow.com/questions/6559358/what-is-the-difference-between-and?rq=1 should help — 4444, Aug 14 '12 at 20:57

score 8 · Accepted Answer · edited Aug 14 '12 at 21:12

8

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).

edited Aug 14 '12 at 21:12

PeeHaa

answered Aug 14 '12 at 20:57

Diego

4

That's not really an answer though. – Lee Taylor Aug 14 '12 at 20:58
I clicked by accident.. sorry. – Diego Aug 14 '12 at 21:00
@Diego Then, if I am comparing variables (of which I don't know the value), should I always use `!==`? – Alexandre Khoury Aug 14 '12 at 21:01
It depends the case. If you have a boolean variable its actually the same. If you have an integer you should use `!==` to compare it with integers or `!=` to "auto cast it" to boolean – Diego Aug 14 '12 at 21:03
`null` never equals `false` in an equality comparison. – Aug 14 '12 at 21:07
@amnotiam You are actually right `(null == false)` is `false`. I got confused because `(null)` (if evaluated as boolean) is `false` and `(!null)` `true`. – Diego Aug 15 '12 at 11:44

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