Map

Map is a collection of elements where each element is stored as a Key, value pair. It can hold both objects and primitive values as either key or value and iterates its elements in insertion order.

Let's take a map with different types of primitives and objects as key-value pairs and various methods on it,

let typeMap = new Map();

var keyObj = {'one': 1}

typeMap.set('10', 'string');   // a string key
typeMap.set(10, 'number');     // a numeric key
typeMap.set(true, 'boolean');  // a boolean key
typeMap.set(keyObj, 'object'); // an object key

console.log(typeMap.get(10));         // number
console.log(typeMap.get('10'));       // string
console.log(typeMap.get(keyObj));     // object
console.log(typeMap.get({'one': 1})); // undefined

console.log(typeMap.size ); // 4

for(let item of typeMap) {
console.log(item);
}

for(let item in typeMap) {
console.log(item);
}