Javascript's associative arrays are nothing but javascript object literals. You can add keys to these objects dynamically if the key is a string using the square brackets notation. For example,
Example
let a = {
name: 'Ayush'
};
let key = 'age';
// Add the non existing key
a[key] = 35;
console.log(a)Output
This will give the output −
{ name: 'Ayush', age: 35 }