Answers for "how to check if a variable is undefined in javascript"

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...");
}

nodejs check if variable is undefined

if ( typeof query !== 'undefined' && query )
{
  //do stuff if query is defined and not null
}
else
{

}

check undefined in javascript

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

undefined javascript check

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