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This article mainly introduces js how to verify undefined and null, the article is very detailed, has a certain reference value, interested friends must read it!

Verify undefined and null

If there is a code like this:

If (a = = null | | a = undefined) {doSomething ()}

That is, if you need to verify that a value is equal to null or undefined, and you need to perform an operation, you can use the null merge operator to simplify the above code:

A?? DoSomething ()

In this way, the code after the control merge operator is executed only if an is undefined or null. The null merge operator is a logical operator that returns its right Operand when the left Operand is null or undefined, otherwise it returns the left Operand.

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