What does === mean?

[bazianm]

Hi.

This is a real newbie question, I think, but I can't seem to find the answer.

I am looking at some javascript code and it uses a triple equal operator. Here's a sample of it:

if (b) return b !== !0 && a.getAttribute("classid") === b

What does that === operator do? I find references to = and == (assign and compare respectively) but I cannot find any reference to ===.

Thanks in advance...

[cations]

=== is an exact match which considers type.

Because JavaScript does type coercion when using == the following statement is true

"2" == 2;  // true

If you want the above statement not to be true use the ===

"2" === 2;  // false

but

2===2;  // true

Some professional web developers such as Doug Crockford recommend using === as much as possible instead of ==.

[handcraftedweb]

I hardly ever use "==" for comparisons, instead use "===". What this means is I simply avoid situations where I would want to know if

"2" == 2 // true
new String == 0 // true
"" == false // true
"" == 0 // true
"" == false // true
new String == false // true
0 == false // true

/*note the logical inconsistency of the following 3 lines*/
"0" == false // true
new String == false // true
new String == "0" // false