when to use === operator check in JavaScript? [duplicate]

This question already has answers here: Closed 12 years ago.

Possible Duplicate:

Javascript === vs == : Does it matter which “equal” operator I use?

As the 开发者_开发技巧title states; when should you use the === operator check when using JavaScript, and when not to.

Edit: more complete answer found here. Thanks to Mark Byers for pointing it out.

_L

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It is strict type equality operator. It not only checks whether two are equal in value but also of the same type.

Consider a situation when you compare numbers or strings:

if (4 === 4) // same value and type
{
  // true
}

but

if (4 == "4") // same value and different type but == used
{
  // true
}

and

if (4 === "4") // same value but different type
{
  // false
}

This applies to objects as well as arrays.

So in above cases, you have to make sensible choice whether to use == or ===

It is good idea to use === when you are sure about the type as well

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When you wish to inhibit implied typecasts. For example:

3 == '3'

is true, whereas this is not:

3 === '3'

Douglas Crockford recommends always using strict comparison.

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You use it to check if a variable's containing value and type is same as the compared one.