check if not undefined javascript code example

Example 1: js if not undefined

if (typeof myVar !== "undefined") {
    console.log("myVar is DEFINED");
}

Example 2: test if is undefined javascript

let id;

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

Example 3: checking if var is not defined js

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

Example 4: js check if undefined

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

Example 5: if not undefined javascript

if(typeof myVar !== "undefined")

Example 6: How can I check whether a variable is defined in Node Js

if (query){
   doStuff();
}