check variable is undefined in javascript code example

Example 1: javascript check for undefined

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

Example 2: checking if var is not defined js

if(typeof x !== 'undefined'){
  alert("Variable x is defined.");
}

Example 3: undefined javascript check

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