Javascript – ExecJS and could not find a JavaScript runtime

Converts Object to boolean. If it was falsey (e.g. 0, null, undefined, etc.), it will be false, otherwise, true.

!oObject  // inverted boolean
!!oObject // non inverted boolean so true boolean representation

So !! is not an operator, it's just the ! operator twice.

Real World Example "Test IE version":

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

If you ⇒

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

But if you ⇒

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

I love 10 ways to format time and date using JavaScript and Working with Dates.

Basically, you have three methods and you have to combine the strings for yourself:

getDate() // Returns the date
getMonth() // Returns the month
getFullYear() // Returns the year

Example:

var d = new Date();
var curr_date = d.getDate();
var curr_month = d.getMonth() + 1; //Months are zero based
var curr_year = d.getFullYear();
console.log(curr_date + "-" + curr_month + "-" + curr_year);