js Undefined code example

Example 1: javascript check for undefined

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

Example 2: javascript if undefined

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

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

} else if(comment === null){

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

}

Example 3: javascript typeof undfined

var x;
if (typeof x === 'undefined') {
   // these statements execute
}

Example 4: undefined javascript check

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

Example 5: javascript check number against undefined

javascript check number against undefined

Example 6: javascript assignment operator if undefined

const variable2 = variable1  || 'new';