JavaScript - add getter to the existing object

In this article, we would like to show you how to add getter to the existing object in JavaScript.

Quick solution:

// ONLINE-RUNNER:browser;

const user = {
  id: '1',
  username: 'Tom',
  role: 'admin',
};

// add getter
Object.defineProperty(user, 'isAdmin', {
  get: function () {
    return this.role == 'admin';
  },
});

console.log(user.isAdmin); // true

Practical example

In this example, we use Object.definePropery() to define the getter for the existing numbers object.

// ONLINE-RUNNER:browser;

const numbers = {
  name: 'prime numbers',
  values: [2, 3, 5, 7],
};

// add getter
Object.defineProperty(numbers, 'last', {
  get: function () {
    if (this.values.length > 0) {
      return this.values[this.values.length - 1];
    }
    return undefined;
  },
});

console.log(numbers.last);  // 7

Output:

7

Related posts

• JavaScript - create object with getter

References

• getter - JavaScript | MDN