How to safely destructure a JavaScript object in TypeScript - Stack Overflow

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I want to pull out attributes from a JavaScript object (below) but want to protect myself from either the object being null or undefined as well as the properties not existing. That is, I want the values to just be undefined and not have the JavaScript error.

const {id,username,userFirstName,userLastName} = attendeeResults;

I want to pull out attributes from a JavaScript object (below) but want to protect myself from either the object being null or undefined as well as the properties not existing. That is, I want the values to just be undefined and not have the JavaScript error.

const {id,username,userFirstName,userLastName} = attendeeResults;

• javascript
• typescript

Share Improve this question Follow asked Feb 6, 2019 at 14:34 PetePete 3,45166 gold badges2828 silver badges5454 bronze badges 1

• If the properties don't exist on the object, undefined is precisely what destructuring will give you, no need to precaution against errors. – Bergi Commented Feb 6, 2019 at 14:47

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5 Answers 5

Sorted by: Reset to default 8

You can use logical operators to achieve that:

const nullObject = null;
const { foo, bar } = nullObject || {};

console.log(foo, bar);

JavaScript allow you to define default value when destructuring an object. For example:

const {id: 0,username:'',userFirstName:'',userLastName:''} = attendeeResults;

But destruncturing throws an error if your attendeeResults object is null or undefined.

This can be done this way:

const {id, username, ...rest} = {id: 10, username: 'u', firstname:'behzad',lastname:'besharati'};


console.log(id,username,rest);

building on the response by José Salgado. Ensure to use ?? Nullish Coalescing Operator since you are actually checking for null

const { foo, bar } = null ?? {};

console.log(foo, bar);

You could use the following, Please notice that i omitted username in the attendee to show that it keeps the null value.

const attendeeResults = { id: 1, userFirstName: 'John', userLastName: 'Smith'}
const obj = {
  id: null,
  username: null,
  userFirstName: null,
  userLastName: null
};
Object.assign(obj, attendeeResults);
console.log(obj);

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