Section 18: ES2016 and ES2017

Question 1

Exponentiation Operator **

Answer 1

two to the power of four

var calculatedNumber = 2**4

calculateNumber; // 16

Question 2

[].includes

Answer 2

var nums = [1,2,3,4,5]

nums. includes(3); // true
nums. includes(44); // false

Question 3

padStart and padEnd

Answer 3

*allows us to designate exactly how long a string should be, and what to use to make it longer if it needs to be lengthened.

“awesome”.padstart(10); // “ awesome”
“awesome”.padstart(10, !); // “!!!awesome”

Question 4

Async Functions and ‘await’ keyword

Answer 4

*Special kind of function that can be paused using the ‘await’ keyword. Await, waits for a promise to be resolved before continuing.

async function getMovieData(){
console.log(“starting!”);
var movieData = await $.getJSON(‘https://omdbapi.com?t=titanic&apikey=thewdb’);
// this line does NOT run until the promise is resolved
console.log(“all done!”);
console.log(movieData);
}

getMovieData() // logs an object with data about the movie!

Question 5

How do you optimize performance while using async functions and ‘await’?

Answer 5

Make sure you’re doing them in parallel rather than sequentially.

async function getMovieData(){
   var titanicPromise = $.getJSON(`https://omdbapi.com?t=titanic&apikey=thewdb`);
   var shrekPromise = $.getJSON(`https://omdbapi.com?t=shrek&apikey=thewdb`);

  var titanicData = await titanicPromise; 
  var shrekData = await shrekPromise; 

console.log(titanicData);
console.log(shrekData);
}

getMovieData();

Question 6

How do you handle errors while using async and await?

Answer 6

You use try/catch statements:

async function getUser(user) {
   try {
        var response = await $.getJSON(`https://api.github.com/users/${user}`);
        console.log(response.name);
    } catch(e){
        console.log("User does not exist!");
    }
}

Question 7

What is a great way to await multiple resolved promises?

Answer 7

** Use the Promise.all operator

async function getMovieData(first, second){
var moviesList = await Promise.all([
$.getJSON(https://omdbapi.com?t=${first}&apikey=thewdb),
$.getJSON(https://omdbapi.com?t=${second}&apikey=thewdb)
]);
console.log(moviesList[0].Year);
console.log(moviesList[1].Year);
}

getMovieData(‘shrek’, ‘blade’);