When should you use === vs ==, !== vs !=, etc.. in javascript? [duplicate]

问题

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Closed 10 years ago.

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

What are the differences between === vs == and !== vs !=?

When should you use each one?

回答1:

=== is the Identity operator, and is used to test that value and type are equal.

so..

"3" == 3 // true
"3" === 3 // false
1 == true // true
1 === true // false
"1" == true // true
"1" === true // false

so when you care that value and type are equal, or not equal use Identity operators === or !==

回答2:

The "normal" == operators in javascript perform type coercion, and try their best to do things like treat a string as number or an object as a string where required. The longer === operators will not do type coercion, but rather a strict comparison within the type.

回答3:

=== and !== are the same as == and !=, but additionally do checks for the variable types.

来源：https://stackoverflow.com/questions/1094531/when-should-you-use-vs-vs-etc-in-javascript