What are Associative Arrays in JavaScript ?

JavaScript Associative arrays are basically objects in which indexes are replaced by user-defined keys. Javascript associative arrays do not have a length property like normal arrays and cannot be traversed using a normal for loop.

Example:

// Creating an associative array (object)
let arr= {
  name: "Geek",
  age: 10,
  city: "Noida"
};
// Accessing values using keys
console.log(person.name);
console.log(person.age);
console.log(person.city); 

We will perform some operations on associative arrays now:

Example 1: In this example, we will Calculate the length of an associative array.

Javascript

let arr = { "apple": 10, "grapes": 20 };
arr["guava"] = 30;
arr["banana"] = 40;

// Printing the array
// returned by keys() method
console.log(Object.keys(arr))

// printing the size
console.log("Size = " + Object.keys(arr).length)

Output

[ 'apple', 'grapes', 'guava', 'banana' ]
Size = 4

Example 2: In this example, we will see how to Sort an Associative Array by its Values

Javascript

let a = []; // Array

// Add elemets to it
a.push({ name: 'a', class: 1 });
a.push({ name: 'b', class: 9 });
a.push({ name: 'c', class: 2 });
a.push({ name: 'd', class: 6 });

// Custom sorting function
let sortedList = a.sort(function (a, b) {
    return a.class - b.class;
});

// Output
console.log(sortedList);

Output

[
  { name: 'a', class: 1 },
  { name: 'c', class: 2 },
  { name: 'd', class: 6 },
  { name: 'b', class: 9 }
]

Example 3: In this example, we will see how to list of associative array keys in JavaScript.

Javascript

// Input Associative Array
let arr = {
    Newton: "Gravity",
    Albert: "Energy",
    Edison: "Bulb",
    Tesla: "AC",
};

// getting keys using getOwnPropertyNames
const keys = Object.getOwnPropertyNames(arr);
console.log("Keys are listed below ");

// Display output
console.log(keys);

Output

Keys are listed below 
[ 'Newton', 'Albert', 'Edison', 'Tesla' ]