Map

In general, dont use unless you need nonstring keys or insertion order

Overview

Map() is funcitonally equivalent to objects but:

• Provides get, set, has, delete, and size methods.

• Accepts any type for the keys instead of just strings.

• Provides an iterator for easy for-of usage and maintains the order of results.

• Doesn't have edge cases with prototypes and other properties showing up during iteration or copying.

• Slower than just objects, b/c js engines compile objects to C++

• Maps can be bigger than objects (16.7M vs 11.1M in Chrome)

• Can be more cumbersome than objects

  • obj[key] += x	
    //vs
    map.set(map.get(key) + x)

  • Harder to debug in console

Usage

const myMap = new Map();

const keyString = 'a string',
    keyObj = {},
    keyFunc = function() {};

// setting the values
myMap.set(keyString, "value associated with 'a string'");
myMap.set(keyObj, 'value associated with keyObj');
myMap.set(keyFunc, 'value associated with keyFunc');

console.log(myMap.size); // 3

// getting the values
console.log(myMap.get(keyString));    
// "value associated with 'a string'"
console.log(myMap.get(keyObj));       
// "value associated with keyObj"
console.log(myMap.get(keyFunc));      
// "value associated with keyFunc"

console.log(myMap.get('a string'));   
// "value associated with 'a string'"
// because keyString === 'a string'
console.log(myMap.get({}));          
// undefined, because keyObj !== {}
console.log(myMap.get(function() {})) 
// undefined, because keyFunc !== function () {}