Maps

All about Maps in JavaScript

  • Similar to Objects in JavaScript
  • Same as dictionaries in Python
  • Same as hashes in Ruby
  • Collection of key-value pairs
    • key's can be any value (including objects)
    • value's can be any data
const myMap = new Map();

Maps vs Objects

MapsObjects
KeysAny data typeStrings only
IterationEasyTricky
SizeEasy to getTricky
PerformanceBetter for large dataBetter for small data

Built-in Functions 🔨

set()

Add key-value pairs to a Map

myMap.set('key1', 'value1'); 
myMap.set('key2', 'value2');
 
// myMap => { 'key1':'value1' , 'key2':'value2' }

get()

Get value by a given key

myMap.get('key1');
// => 'value1'

has()

Checks if a key exists in the map.

myMap.has('key1'); // output: true 
myMap.has('key2'); // output: false

keys()

Returns an iterator over the keys in the map

for (const key of myMap.keys()) { 
    console.log(key);
}
// =>
// key1
// key2

values()

for (const value of myMap.values() ) { 
    console.log(value); 
}
// =>
// value1
// value2

entries()

Returns an iterator object (e.g Array) with the [key, value] pairs in a Map

for (const [key, value] of myMap.entries() ) { 
   console.log(`${key} = ${value}`);
}
// =>
// key1 = value1 
// key2 = value2

forEach()

Allows iterate over key-value pairs in the Map

myMap.forEach( (value, key) => { 
    console.log(`${key} = ${value}`);
});
// =>
// key1 = value1 
// key2 = value2

size

Property: Returns the number of key-value pairs in the map.

myMap.size; 
// => 2

delete()

  • Removes a pair in the Map
fruits.delete("key1");

clear()

Removes all the elements from the Map

fruits.remove()