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 funcational difference, if there is one? Is one superior to the other? What, if any, are the conditions for picking to use one versus the other?

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.

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

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