How to get a subset of a javascript object's properties?

To get a subset of an object's properties and create a new object with selected properties, you can use object destructuring combined with property shorthand. This technique allows you to extract specific properties and create a new object containing only those properties.

Basic Example

Let's start with an object containing multiple properties:

const person = {
    name: 'John',
    age: 40,
    city: 'LA',
    school: 'High School'
};

// Extract only name and age
const {name, age} = person;
const selectedObj = {name, age};
console.log(selectedObj);

{ name: 'John', age: 40 }

Method 1: Destructuring with Property Shorthand

The most concise approach combines destructuring and property shorthand in one line:

const person = {
    name: 'Alice',
    age: 25,
    email: 'alice@example.com',
    phone: '123-456-7890',
    address: 'New York'
};

// Create subset with name, email, and phone
const subset = (({name, email, phone}) => ({name, email, phone}))(person);
console.log(subset);

{ name: 'Alice', email: 'alice@example.com', phone: '123-456-7890' }

Method 2: Using Object.pick Function

For reusability, create a helper function that picks specific properties:

function pick(obj, keys) {
    return keys.reduce((result, key) => {
        if (key in obj) {
            result[key] = obj[key];
        }
        return result;
    }, {});
}

const user = {
    id: 1,
    username: 'johndoe',
    password: 'secret123',
    email: 'john@example.com',
    createdAt: '2023-01-01'
};

// Pick only safe properties to send to client
const publicUser = pick(user, ['id', 'username', 'email']);
console.log(publicUser);

{ id: 1, username: 'johndoe', email: 'john@example.com' }

Method 3: Using Rest Operator to Exclude Properties

Sometimes it's easier to exclude specific properties rather than include them:

const apiResponse = {
    data: 'important info',
    status: 200,
    timestamp: '2023-12-01',
    internalId: 'xyz123',
    debugInfo: 'sensitive data'
};

// Exclude internal properties
const {internalId, debugInfo, ...publicData} = apiResponse;
console.log(publicData);

{ data: 'important info', status: 200, timestamp: '2023-12-01' }

Comparison

Conclusion

Object destructuring with property shorthand is the most common approach for creating object subsets in JavaScript. For dynamic scenarios, use a pick function, and when you need to exclude only a few properties, the rest operator provides an elegant solution.