An Easy and better way to check for null and undefined values in JavaScript

Published July 15, 2020

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In many cases, we have null or undefined values in our variables. We can conditionally show other relevant value using the new ?? (Nullish coalescing) operator instead of just showing null or undefined values.

Consider these variables name with the value of null and age with the value of 23.

// name and age variables
let name = null;
let age = 23;

Now if we try to view the values using the console.log() method it would show null and 23 in the console.

// name and age variables
let name = null;
let age = 23;

console.log(name, age);

But we don't want an unpredictable behavior like that.

Let's now remove that unpredictable behavior using the ?? operator.

// name and age variables
let name = null;
let age = 23;

// using ?? operator
console.log(name ?? "Anonymous", age ?? "Age not defined");

Now if we try to view the variables we can see that when showing the name variable it shows Anonymous and for the age variable it shows the number 23.

This is what the ?? operator does.

It checks if a variable has null or undefined values and if it does contain those values it doesn't take that value and gives it what comes after the ?? operator. In our case Anonymous value.

Now if you try to change the age value to undefined.

it will show,

Age not defined

🚨 NOTE: The ?? operator only checks if values are null or undefined. It doesn't check for boolean values true, false 1 or 0. To check for boolean values you may need to use the || (OR operator) or && (AND operator).

⚠️ NOTE: This operator is a new addition to JavaScript. You may need to use polyfills to work with older browsers.

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