To access the object property dynamically in JS, you need to pass the property name as a string in square brackets.

const user = {
  age: 25,
  name: 'Jack'

let key = 'age';

console.log(user[key]);  // 25

key = 'name';

console.log(user[key]);  // Jack

As the value of the variable key changed, we got access to the different properties of the user object.

The most common way to access the object properties in JavaScript is the dot. You write something like user.age or to get access to the properties age and name of the object user.

It works perfectly until you need to design an algorithm that doesn’t know in advance which property it needs to access.