Answers for "compare undefined in javascript"

javascript if undefined

if(typeof comment === 'undefined') {

  alert('Variable "comment" is undefined.');

} else if(comment === null){

  alert('Variable "comment" is null.');

}

how to check if object is undefined in javascript

if (typeof something === "undefined") {
    alert("something is undefined");
}

assign this value or if it is undefined this other value javascript

var x; //variable to change
var y; //higher priority variable
var z = 12; //lower priority variable
x = !(y === undefined) ? y : z;
console.log(x); //12