Question

Possible Duplicates:
myVar = !!someOtherVar
What does the !! operator (double exclamation point) mean in JavaScript?

Came across this line of code

strict = !!argStrict

… here and wondered what effect the !! has on the line? Pretty new to JS!

Answer 1

It converts your value to a boolean type:

var x = '1';
var y = !!x;

// (typeof y === 'boolean')

Also note the following:

var x = 0;
var y = '0';       // non empty string is truthy
var z = '';

console.log(!!x);  // false
console.log(!!y);  // true
console.log(!!z);  // false