ECMAScript 2017
Original JavaScript version numbers were ES5 (2009) and ES6 (2015).
Since 2016, versions are named by year: ECMAScript 2016, 2017, 2018, 2019.
New Features in ECMAScript 2017
This chapter introduces the new features in ECMAScript 2017:
- JavaScript String padding
- JavaScript Object entries()
- JavaScript Object values()
- JavaScript async and await
- JavaScript Object.getOwnPropertyDescriptors
JavaScript String Padding
ECMAScript 2017 added two String methods: padStart
and padEnd to support padding at the beginning and at the end of a string.
Examples
let text = "5";
text = text.padStart(4,0);
Try it Yourself »
let text = "5";
text = text.padEnd(4,0);
Try it Yourself »
JavaScript string padding is supported in all modern browsers since April 2017:
| Chrome 57 | Edge 15 | Firefox 48 | Safari 10 | Opera 44 |
| Mar 2017 | Apr 2017 | Aug 2016 | Sep 2016 | Mar 2017 |
JavaScript Object Entries
ECMAScript 2017 added the Object.entries() method to objects.
Object.entries() returns an array of the key/value pairs in an object:
Example
const person = {
firstName : "John",
lastName : "Doe",
age : 50,
eyeColor : "blue"
};
let text = Object.entries(person);
Try it Yourself »
Object.entries() makes it simple to use objects in loops:
Example
const fruits = {Bananas:300, Oranges:200, Apples:500};
let text = "";
for (let [fruit, value] of Object.entries(fruits)) {
text += fruit + ": " + value + "<br>";
}
Try it Yourself »
Object.entries() also makes it simple to convert objects to maps:
Example
const fruits = {Bananas:300, Oranges:200, Apples:500};
const myMap = new Map(Object.entries(fruits));
Try it Yourself »
Object.entries() is supported in all modern browsers since March 2017:
| Chrome 47 | Edge 14 | Firefox 47 | Safari 10.1 | Opera 41 |
| Jun 2016 | Aug 2016 | Jun 2016 | Mar 2017 | Oct 2016 |
JavaScript Object Values
Object.values() are similar to Object.entries(),
but returns a single dimension array of the object values:
Example
const person = {
firstName : "John",
lastName : "Doe",
age : 50,
eyeColor : "blue"
};
let text = Object.values(person);
Try it Yourself »
Object.values() is supported in all modern browsers since March 2017:
| Chrome 54 | Edge 14 | Firefox 47 | Safari 10.1 | Opera 41 |
| Oct 2016 | Aug 2016 | Jun 2016 | Mar 2017 | Oct 2016 |
JavaScript Async Functions
Waiting for a Timeout
async function myDisplay() {
let myPromise = new Promise(function(myResolve, myReject) {
setTimeout(function() { myResolve("I love You !!"); }, 3000);
});
document.getElementById("demo").innerHTML = await myPromise;
}
myDisplay();
Firefox and Chrome were the first browsers with support for async JavaScript functions:
| Chrome 55 | Edge 15 | Firefox 52 | Safari 11 | Opera 42 |
| Dec 2016 | Apr 2017 | Mar 2017 | Sep 2017 | Dec 2016 |
