Answers for "double exclamation mark js"

javascript on double click

document.getElementById("myBtn").addEventListener("dblclick", function() {
  alert("Hello World!");
});

javascript double question mark

let a = null;
const b = a ?? -1;		// Same as b = ( a != null ? a : -1 );
console.log(b);		  	// output: -1
//OR IF
let a = 9;
const b = a ?? -1;
console.log(b);  		// output: 9

//PS.,VERY CLOSE TO '||' OPERATION IN FUNCTION, BY NOT THE SAME

javascript double exclamation mark

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

javascript double exclamation mark

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

javascript double exclamation mark

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