node if undefined code example

Example 1: javascript check for undefined

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

Example 2: test if is undefined javascript

let id;

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

Example 3: js check if undefined

let foo = undefined
//will return true
typeof foo === 'undefined'

Example 4: How can I check whether a variable is defined in Node Js

if (query){
   doStuff();
}