JavaScript: Exploring Map data structure

JavaScript provides Map data structure, it is used to store the elements in <key, value> pairs and iterate over the elements in insertion order.

How to create a map?

Use the Map constructor to define an instance of Map class.

Syntax

new Map([iterable])

iterable can be an Array or other iterable object whose elements are key-value pairs.

Example 1

HelloWorld.js

var countriesMap = new Map();

countriesMap.set("Bahrain", "Manama");
countriesMap.set("Cameroon", "Yaounde");
countriesMap.set("Norway", "Oslo");
countriesMap.set("India", "New Delhi");

for (var [country, capital] of countriesMap) {
  console.log(country + ' : ' + capital);
}

Output

Bahrain : Manama

Cameroon : Yaounde

Norway : Oslo

India : New Delhi

Example 2:

HelloWorld.js

var countries = [["Russia", "Moscow"], ["Spain", "Madrid"]];

var countriesMap = new Map(countries);

countriesMap.set("Bahrain", "Manama");
countriesMap.set("Cameroon", "Yaounde");
countriesMap.set("Norway", "Oslo");
countriesMap.set("India", "New Delhi");

for (var [country, capital] of countriesMap) {
  console.log(country + ' : ' + capital);
}

Output

Russia : Moscow

Spain : Madrid

Bahrain : Manama

Cameroon : Yaounde

Norway : Oslo

India : New Delhi

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