Question

Reading through some code, I came across the use of !0 and !1. I realize that these are shorter ways of writing true and false.

!0 === true
!1 === false

This of course save a few bytes, but is there some other reason to use it?

Is there a name for this way of writing it?

Answer 1

Most JavaScript minification tools, like UglifyJS, generate that code because it’s shorter and semantically equivalent. For example, given:

var x = true;
if (x) { 
  alert(x); 
}

UglifyJS will generate var x=!0;x&&alert(x).

Usually, you don’t need to write code using that style; let the minifiers do their work :-).