when to use === operator check in JavaScript?

2018-05-30 02:22:53

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

As the 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.

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

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.

你用它来检查一个变量的包含值和类型是否与被比较的变量相同。

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