Creating & Modifying Maps

Maps

If Sets are similar to Arrays, then Maps are similar to Objects because Maps store key-value pairs similar to how objects contain named properties with values.

Essentially, a Map is an object that lets you store key-value pairs where both the keys and the values can be objects, primitive values, or a combination of the two.

How to Create a Map

To create a Map, simply type:

const employees = new Map();
console.log(employees);

Map {}

This creates an empty Mapemployeewith no key-value pairs.

Modifying Maps

Unlike Sets, you can’t create Maps from a list of values; instead, you add key-values by using the Map’s.set()method.

const employees = new Map();

employees.set('[email protected]', { 
    firstName: 'James',
    lastName: 'Parkes',
    role: 'Content Developer' 
});
employees.set('[email protected]', {
    firstName: 'Julia',
    lastName: 'Van Cleve',
    role: 'Content Developer'
});
employees.set('[email protected]', {
    firstName: 'Richard',
    lastName: 'Kalehoff',
    role: 'Content Developer'
});

console.log(employees);

Map {'[email protected]' => Object {...}, '[email protected]' => Object {...}, '[email protected]' => Object {...}}

The.set()method takes two arguments. The first argument is the key, which is used to reference the second argument, the value.

To remove key-value pairs, simply use the.delete()method.

employees.delete('[email protected]');
employees.delete('[email protected]');
console.log(employees);

Map {'[email protected]' => Object {firstName: 'James', lastName: 'Parkes', role: 'Course Developer'}}

Again, similar to Sets, you can use the.clear()method to remove all key-value pairs from the Map.

employees.clear()

console.log(employees);

Map {}

TIP: If you.set()a key-value pair to a Map that already uses the same key, you won’t receive an error, but the key-value pair will overwrite what currently exists in the Map. Also, if you try to.delete()a key-value that is not in a Map, you won’t receive an error, and the Map will remain unchanged.

The.delete()method returnstrueif a key-value pair is successfully deleted from theMapobject, andfalseif unsuccessful. The return value of.set()is theMapobject itself if successful.