JAVASCRIPT

javascript check if not undefined

if (typeof myVar !== "undefined") {
    console.log("myVar is DEFINED");
}

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...");
}

javascript check if undefined

let myVar;

if (myVar === undefined){}
  //!! Note: myVar == undefined would also check wether myVar is null 

//alternatively
if (typeof myVar === 'undefined'){ }

check undefined in javascript

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

js check if undefined

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

javascript check undefined

if(myVar === null) {
	console.log("Element is undefined");
}

javascript test if undefined

if (angular.isDefined(var){
    //myVariable is undefined
}

javascript check if undefined

const obj =
{
  "name": "John Doe",
  "age": 39,
  "Street": "Hauptstraße 5"
}
// street is undefined (its uppercase)
var { name: fullname, age, street } = obj;

// You need an array [...]
// if you will check one variable
TestUndef([age]);
// or more
TestUndef([fullname, street, age]);

console.log("All Ok");

function TestUndef(what) {
  for (var that of what) {
    if (typeof (that) == "undefined") {
      throw new Error(`UNDEFINDED OBJECTS!`);
    }
  }
}
// no write "street" in line 5 lowercase, then its all ok.