JavaScript Maps Overview

A Map in JavaScript is a collection of key-value pairs where keys can be of any data type, unlike objects where keys are typically strings or symbols. Maps maintain insertion order, making them suitable for storing structured data with flexible key types.

• Any Key Type: Keys can be objects, functions, numbers, or strings.
• Ordered: Keys are iterated in the order of insertion.
• Size Property: .size returns the number of entries.
• Iterable: Maps can be looped using for...of, forEach, or spread operators.
• Better Performance: For frequent additions and removals, Maps are often more efficient than plain objects.

Creating Maps

a. Using Map Constructor

const map = new Map();
map.set('name', 'Alice');
map.set(1, 'Number Key');
map.set(true, 'Boolean Key');

b. Using an Array of Key-Value Pairs

const map = new Map([
  ['name', 'Alice'],
  [1, 'Number Key'],
  [true, 'Boolean Key']
]);

Map Methods

Iterating Over a Map

a. Using for...of

for (const [key, value] of map) {
  console.log(key, value);
}

b. Using .forEach()

map.forEach((value, key) => {
  console.log(key, value);
});