Optional chaining in JavaScript

Published July 17, 2020

Optional chaining operator (?.) is a new addition in JavaScript where it helps to checks if a property, method etc is present or not.

Let's look at an example to get to know more.

Let's create an object called John with the properties name and age.

// John object
const John = {
  name: "John Doe",
  age: 23,
};

Now, what if we tried to access a property called address which is not in the John object. Yeah, you're right it will show undefined.

But that's OK-ish? Because at least this can be checked with an if statement like this.

// John object
const John = {
  name: "John Doe",
  age: 23,
};

// this checking is ok for now
if (John.address) {
  console.log(John.address);
} else {
  console.log("Address property is not defined");
}

But oftentimes programmers in JavaScript tend to access more properties inside the address property and this makes things worse 😟. Because now JavaScript will throw a huge error instead of Address property is not defined.

Let's try to access another property called street inside the address property.

Try executing this code now,

// John object
const John = {
  name: "John Doe",
  age: 23,
};

// this will throw an error 🚫
// since the address property is not defined
// and we are tring to access another property of street
// inside the address property which itself is undefined 🚨
if (John.address.street) {
  console.log(John.address.street);
} else {
  console.log("Address property is not defined");
}

That's where the use of the newly introduced ?. optional chaining operator comes in.

The ?. operator will check if the property is present and returns property if present and returns undefined if it is not present.

The ?. operator is added after a property name that we want to check for.

eg: John.address?.street

Let's look at it now,

// John object
const John = {
  name: "John Doe",
  age: 23,
};

// the ?. operator will check for the presence of property
// here, the  else statement will be executed
// instead of throwing an error
if (John.address?.street) {
  console.log(John.address.street);
} else {
  console.log("Address property is not defined");
}

Before optional chaining operator programmers used to do this kind of checks with the && (AND) operator like this.

// John object
const John = {
  name: "John Doe",
  age: 23,
};

// using AND operator
// instead of ?. operator
if (John && John.address && John.address.street) {
  console.log(John.address.street);
} else {
  console.log("Address property is not defined");
}

The ?. operator can also be used to check for methods present in an object.

Suppose you are trying to call a method called sayHello which is not defined in the John object.

// John object
const John = {
  name: "John Doe",
  age: 23,
};

// call sayHello() method
// which is not defined
John.sayHello();

It will throw an error saying TypeError: John.sayHello is not a function.

Let's check it with ?. operator.

// John object
const John = {
  name: "John Doe",
  age: 23,
};

// call sayHello() method
// but now checking with ?. operator
// and the method is not called ✅
John.sayHello?.();

Feel free to share if you found this useful 😃.


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