Answers for "javascript if undefined then"

Javascript check if undefined

if (typeof myVariable === 'undefined'){
    //myVariable is undefined
}

javascript if undefined

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

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

} else if(comment === null){

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

}

test if is undefined javascript

let id;

if(typeof id === 'undefined') {
    console.log("id 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

js check if undefined

let foo = undefined
//will return true
typeof foo === 'undefined'

javascript set variable if not defined

var x = (typeof x === 'undefined') ? your_default_value : x;