ES7

Arrow functions

spread ...

let { x, y, ...z } = { x: 1, y: 2, a: 3, b: 4 };
console.log(x); // 1
console.log(y); // 2

console.log(z); // { a: 3, b: 4 }

Text

https://stackblitz.com/edit/react-class-example-map

https://medium.com/front-end-hacking/es6-map-vs-object-what-and-when-b80621932373

Weak Map

WeakMaps help developers avoid memory leaks by holding references to their properties weakly, meaning that if a WeakMap is the only object with a reference to another object, the GC may collect the referenced object.

https://stackoverflow.com/questions/29413222/what-are-the-actual-uses-of-es6-weakmap

Weak set

By definition, WeakSet has only three key functionalities

Weakly link an object into the set
Remove a link to an object from the set
Check if an object has already been linked to the set

WeakSet objects are collections of objects. An object in the WeakSet may occur only once; it is unique in the WeakSet's collection.

The main differences to the Set object are:

In contrast to Sets, WeakSets are collections of objects only and not of arbitrary values of any type.
The WeakSet is weak: References to objects in the collection are held weakly. If there is no other reference to an object stored in the WeakSet, they can be garbage collected. That also means that there is no list of current objects stored in the collection. WeakSetsare not enumerable.

forEach() — executes a provided function once for each array element.
map() — creates a new array with the results of calling a provided function on every element in the calling array.

Map, forEach

arr.forEach((num, index) => {
    return arr[index] = num * 2;
});

// arr = [2, 4, 6, 8, 10]

let doubled = arr.map(num => {
    return num * 2;
});

// doubled = [2, 4, 6, 8, 10]

filter

find, findIndex

let arr = ['a','b','c'];
arr.findIndex(k => k=='b');
// 1

arr.findIndex(k => k=='z');

// -1

if(arr.findIndex(k => k=='z') > 0)

let arr = [2, 4, 6, 8, 9, 10, 12];
function isOdd(i) {
  return i % 2 !== 0;
}
arr.findIndex(isOdd);
// 4

let arr = ['a','b','c'];
arr.find(k => k=='b');
// 'b'

https://stackblitz.com/edit/react-class-example-find

function resolveAfter2Seconds() {
  return new Promise(resolve => {
    setTimeout(() => {
      resolve('resolved');
    }, 2000);
  });
}

async function asyncCall() {
  console.log('calling');
  var result = await resolveAfter2Seconds();
  console.log(result);
  // expected output: 'resolved'
}

asyncCall();

Promises, async

Bind

ES7