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JS Objects

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JS Classes

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JS Async

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JS HTML DOM

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JS JSON

JSON Intro JSON Syntax JSON vs XML JSON Data Types JSON Parse JSON Stringify JSON Objects JSON Arrays JSON Server JSON PHP JSON HTML JSON JSONP

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JS References

JavaScript Objects HTML DOM Objects


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

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);
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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);
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();

Try it Yourself »

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