What Is The Difference Between If(!!condition) And If(condition)

I often see code that uses !!condition as opposed to just the regular condition. I.e.: if(!!value){ doSomething(); } versus: if(value){ doSomething(); } What is the funca

Solution 1:

Technically nothing. The double bang !! type converts value to a boolean - something the if statement does when it evaluates value anyway.

In the code you have posted, the !! is useless and serves no purpose.

Solution 2:

This is just a more explicit way to test the "truthiness" of a value.

The following will "cast" value to a boolean.

!!(value)

For example, a non-empty string

!!"a" // true

Another example with an empty string

!!"" // false

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However, if you simply test a value directly using

if (value) // ...

then the following values are false in JavaScript

• 0
• -0
• null
• "" (empty string)
• false
• undefined
• NaN

everything else is true

Solution 3:

The !! ensures the resulting type is a boolean (true or false).

javascript:alert("foo") --> foo

javascript:alert(!"foo") --> false

javascript:alert(!!"foo") --> true

javascript:alert(!!null) --> false

They do this to make sure $('row') isn't null.

It's shorter to type than $('row') != null ? true : false.