Js!! The function of a conditional judgment or operation

Source: Internet
Author: User

It's very strange to see a judgment statement today:

1 if (!! Selected) {}//Why is it double '! ' What's the number?

I checked the information and finally understand the principle:

Original '!! ' Converts an expression to a Boolean type of data.

If '!undefined '//is true but to prevent the value from being equal to undefined, we can use '!! ' to judge;

In fact, '! ' is to exclude {non-null/undefined/0/'} equivalent;

Such as

var obj = {Flag:true};var Demo =!! Obj.flag; Demo equals True


Js!! The function of a conditional judgment or operation

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