Help please 😓😓😓

Question

I’m reading a book about js, and in a library I found this peace of code:

CanvasRenderingContext2D.prototype.cartesian = function(on)
{
this.iscartesian = !!on;
return this;
}

So, what is the meaning of “!!”?

Answer 1

It is a trick to force the value of on to be boolean. Zero is false and non-zero is true. If on has 5, !5 becomes false and !!5 becomes true so iscartesian will only have true or false values.

Answer 2

@maxcookmax I click on the star before I reply so I get notification of other people responding. I also refresh the thread afterwards because notifications can be delayed. However, having multiple right answers are not a problem. Better that over none.

Answer 3

@John thank you very much, very helpful.
@maxcookmax Thank you too, I will try.

I have one other question, Does this trick works in other programming languages??

Answer 4

In some, yes. Others, do not support implicit typecasts and generate errors.

Answer 5

Thank you again John