Name: 💡 How to check if a variable is undefined in JS
Rating: 4 (1150 reviews)
Author: benjaminmock

💡 How to check if a variable is undefined in JS

Benjamin Mock - Jan 22 '20 -

How do I check if a variable is undefined in JavaScript?

tldr

typeof xyz === "undefined"
// ==> true

You might be tempted to check a variable with something like

if(!xyz) {
    // this will NOT WORK! It crashes because xyz is not defined
    console.log("not defined");
}

Doing so will lead to an error like the following:

Uncaught ReferenceError: xyz is not defined

So the solution is, as already mentioned to use the typeof operator