if var is undefined javascript 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: test if is undefined javascript

let id;

if(typeof id === 'undefined') {
    console.log("id is undefined...");
}

Example 4: check if variable is undefined or null jquery

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

Example 5: nodejs check if variable is undefined

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

}

Example 6: if not undefined javascript

if(typeof myVar !== "undefined")