javscript check if variable is undefined code example

Example 1: javascript if undefined

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

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

} else if(comment === null){

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

}

Example 2: check if variable is undefined or null jquery

if (variable == null) {
    // variable is either null or undefined
}

Example 3: javascript check undefined

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

Example 4: undefined javascript check

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