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JavaScript ECMAScript 2017

Original JavaScript version numbers were ES5 (2009) and ES6 (2015)

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 functions
  • JavaScript shared memory

    • 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.

    Example

    let str = "5";
    str = str.padStart(4,0);
    // result is 0005

    Example

    let str = "5";
    str = str.padEnd(4,0);
    // result is 5000

    String Padding is not supported in Internet Explorer.

    Firefox and Safari were the first browsers with support for JavaScript string padding:

    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 adds a new Object.entries method to objects.

    The Object.entries() method returns an array of the key/value pairs in an object:

    Example

    const person = {
      firstName : "John",
      lastName : "Doe",
      age : 50,
      eyeColor : "blue"
    };
    document.getElementById("demo").innerHTML = Object.entries(person);

    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 + "
    ";
    }

    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));

    Chrome and Firefox were the first browsers with support for Object.entries:

    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"
    };
    document.getElementById("demo").innerHTML = Object.values(person);

    Firefox and Chrome were the first browsers with support for Object.values:

    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

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