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Muhammad Saim Hashmi
Muhammad Saim Hashmi

Posted on • Edited on

Difference between ? and ?? in JavaScript/Typescript

#javascript #operators #optional #typescript

Hey folks, if you have opened this article that means you are curious about these 2 operators, how they operate, and what's the difference between these two. So without wasting any time, let's jump into details with a code example.

?

? is Optional Chaining Operator, also commonly named as null checker for objects. Its primary use is to check if an object exists or not.

Example

const user = {
    id: 5,
    name: "John"
};
console.log(user?.name); //John
console.log(user?.fullName); //undefined, program won't crash.
console.log(user.fullName); 
//TypeError: Cannot read property ‘fullName’ of undefined
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??

?? is Nullish Coalescing Operator. It is used to initialize an object/variable if it is undefined or null.

Example

const user = {
    id: 5,
    name: "",
    firstName: null,
    lastName: undefined
};
console.log(user.name??"Johnny Depp");// prints ""
console.log(user.firstName??"Johnny");// prints Johnny
console.log(user.lastName??"Depp");// prints Depp
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Feel free to add suggestions in the comments.
Thanks. Happy Coding.

Top comments (20)

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noriller profile image
Bruno Noriller •

Hey!
I know what you meant, but the user.fullName don't crash. It just returns undefined.
For it to crash you would need user.fullName.somethingElse.

This is because the user object exists and it's not a problem to try access keys that don't exist.

Also, this could be translation issues, but ?? works as ||, except, as you said, only with null and undefined.

As a tip: use 3 backticks (`) plus the language to print code:

// ts example here
// just add "ts" after the backticks
const script: Language = "javascript";
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saimwebhr profile image
Muhammad Saim Hashmi •

Great, thanks for the correction Bruno.

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tasin5541 profile image
Miftaul Mannan •

Another thing to keep in mind when you're checking for empty string (i.e ""). Nullish Coalescing Operator (??) will return false only if the variable is null. But Optional Chaining Operator (?) will return false if either the value is null or if it's an empty string.

var name = "";

console.log("hello", name  ? name : "empty");
// hello empty

console.log("hello", name  ?? "empty");
// hello
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var name = null;

console.log("hello", name  ? name : "empty");
// hello empty

console.log("hello", name  ?? "empty");
// hello empty
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saimwebhr profile image
Muhammad Saim Hashmi •

Great, thanks

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sagaryal profile image
Sagar Aryal •

Just to clarify below code is Not Optional Chaining Operator but Ternary operator.

console.log("hello", name  ? name : "empty");
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devmando profile image
CodeFilez •

You learn something everyday! :)

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saimwebhr profile image
Muhammad Saim Hashmi •

Learning never stops :))

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kievandres profile image
Kiev Andres •

Thanks for the article!

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srnascimento40 profile image
SrNascimento40 •

Nice, i didn't know "??" Seems very helpful

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saimwebhr profile image
Muhammad Saim Hashmi •

Do give it a shot.

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gajjardarshithasmukhbhai profile image
Darshit Gajjar • • Edited

I love this article ❤️❤️

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saimwebhr profile image
Muhammad Saim Hashmi •

Glad to hear it.

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akhan763 profile image
Ali Khan •

Such an informational feed!

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saimwebhr profile image
Muhammad Saim Hashmi •

Thanks a lot buddy.

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yashraj021 profile image
Yash •

It returns true for 0 and false for Unknown and Null

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x3daniking profile image
Adnan Khan •

Wow, thanks dude for the gain

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saimwebhr profile image
Muhammad Saim Hashmi •

Most welcome. Follow me for more articles. Happy Friday.

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quannh2 profile image
Quan Nguyen •

Clear information. Thanks!

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saimwebhr profile image
Muhammad Saim Hashmi •

I'm happy to help.

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