ES2015-Map.md

title	category	tags	date
[ES2015] Map object	JavaScript	ES2015 Concepts	2016-12-22

Map

The Map object is a simple key/value map. Any value (both objects and primitive values) may be used as either a key or a value.

You set and get values to/from a Map.

'use strict';

let classroom = new Map();

let stevenJ = { name: 'Steven', age: 22 },
    sarah = { name: 'Sarah', age: 23 },
    stevenS = { name: 'Steven', age: 22 };

classroom.set('stevenJ', stevenJ)
classroom.set('sarah', sarah)
classroom.set('stevenS', stevenS)

console.info('classroom size: ', classroom.size) // classroom size: 3

if (classroom.has('stevenJ')) console.log('stevenJ is in the classroom') // stevenJ is in the classroom

console.log('sarah', classroom.get('sarah')) // sarah: { name: 'Sarah', age: 23 } 
classroom.delete('sarah')
console.log('sarah:', classroom.get('sarah')) // sarah: undefined

for (let student of classroom) {
  console.log(`${student[0]}: ${student[1].name} is ${student[1].age} years old`)
}
// stevenJ: Steven is 22 years old            
// stevenS: Steven is 22 years old

console.info('classroom size: ', classroom.size) // classroom size: 2
classroom.clear()
console.info('classroom size: ', classroom.size) // classroom size: 0

To empty a Set or Map object of all stored values, you can use the clear() method.

Map vs. Set

Maps can include Sets. Links

• Treehouse: Map
• MDN: Map