ES6: Maps and WeakMaps

Maps

If sets are to an array, maps are to an object

It has a key and a value instead of just values

const dogs = new Map();

- Call .set() to add something

dogs.set('Woofer',3);
dogs.set('Bowwower',5);

- .has() to check key
dogs.has('Woofer');
-true

- .get() to get value
dogs.get('Woofer');
-3

- .delete() to remove item
dogs.delete('Woofer');

You can iterate over Maps in 2 ways:
1.Use a forEach loop
dogs.forEach((val,key)=>console.log(val,key));
-Gives us all dogs
2.Use a for of loop
for(const dog of dogs){
    console.log(key,val);
}
//Can use destructing here
for(const [key,val] of dogs){
    console.log(key,val);
}
-Gives us an array of dogs

dogs.clear();

Useful for Meta-data tracking

We can use the object itself to get values instead of key strings

const clickCounts = new Map;

const buttons = document.querySelectorAll(‘button’);

buttons.forEach(button => clickCounts.set(button,0

button.addEventListener(‘click’, function(){

const val = clickCounts.get(this);

console.log(val);

clickCounts.set(this,val+1);

console.log(clickCounts);

});

));

WeakMap

Setting to null gets garbage collected, just like WeakSet