double exclamation meaning in javascript code example

Example 1: javascript double exclamation mark

const isIE8 = !! navigator.userAgent.match(/MSIE 8.0/);  
console.log(isIE8); // returns true or false

Example 2: javascript double exclamation mark

console.log(navigator.userAgent.match(/MSIE 8.0/));  
// returns either an Array or null