ECMAScript 2017

JavaScript Version Numbers

Old JS versions are named by numbers: ES5 (2009) and ES6 (2015).

From 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 to JavaScript: 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);

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let text = "5";
text = text.padEnd(4,0);

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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);

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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>";
}

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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));

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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);

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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();

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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

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