Answers by Sentry

Removing Properties from Objects in JavaScript

Pieter E.

The Problem

You have an object with several properties and you want to remove some of these properties before using the object further.

    let person = {
        firstName: "John",
        lastName: "Doe",
        gender: "Male",
        age: 34
    };

    const json = JSON.stringify(person);
    console.log(json);
    // => {"firstName":"John","lastName":"Doe","gender":"Male","age":34}
    // What can we do if we don't want the `age` property in the JSON string? -->

Here the JSON string also contains the age property. However, you will be sending the string over the network, and the server on the other end won’t be using the age property. So you want to remove the age property from the person object before converting it to a JSON string.

The Solution

You can use the delete operator, which is simpler, or object destructuring, which can remove more than a single property at a time.

Using the delete operator

Use the delete operator to remove a property from an object.

    let person = {
        firstName: "John",
        lastName: "Doe",
        gender: "Male",
        age: 34
    };

    // Delete the age property first
    delete person.age;
    let json = JSON.stringify(person);
    console.log(json);

The delete operator will return if it was successful and always returns true - even when a property does not exist. The call will only return false when a property is non-configurable - which is the case for properties on built-in objects like the length of an Array.

Using object destructuring

The delete operator can only remove one property per call. So if you want to delete the age and gender properties, then you have to make two delete calls. As an alternative, you can use object destructuring to remove multiple properties with one call.

    const person = {
        firstName: "John",
        lastName: "Doe",
        gender: "Male",
        age: 34
    };

    // Destructure the age and gender
    const {age, gender, ...personTrimmed} = person;
    const json = JSON.stringify(personTrimmed);
    console.log(json);

Note that destructuring is significantly slower than the delete operator because it makes a new object copy from the original object. Destructuring is also not supported by any versions of IE.

Further Reading

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