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ECMAScript 2019

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

Since 2016, versions are named by year: ECMAScript 2016, 2017, 2018, 2019, 2020.

New Features in ES2019

Warning

These features are relatively new. Old browser may need an alternative code (Polyfill)


JavaScript String trimStart()

ES2019 added the String method trimStart() to JavaScript.

The trimStart() method works like trim(), but removes whitespace only from the start of a string.

Example

let text1 = "     Hello World!     ";
let text2 = text1.trimStart();
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JavaScript String trimStart() is supported in all browsers since January 2020:

Chrome 66 Edge 79 Firefox 61 Safari 12 Opera 50
Apr 2018 Jan 2020 Jun 2018 Sep 2018 May 2018

JavaScript String trimEnd()

ES2019 added the String method trimEnd() to JavaScript.

The trimEnd() method works like trim(), but removes whitespace only from the end of a string.

Example

let text1 = "     Hello World!     ";
let text2 = text1.trimEnd();
Try it Yourself »

JavaScript String trimEnd() is supported in all browsers since January 2020:

Chrome 66 Edge 79 Firefox 61 Safari 12 Opera 50
Apr 2018 Jan 2020 Jun 2018 Sep 2018 May 2018

JavaScript Object fromEntries()

ES2019 added the Object method fromEntries() to JavaScript.

The fromEntries() method creates an object from iterable key / value pairs.

Example

const fruits = [
["apples", 300],
["pears", 900],
["bananas", 500]
];

const myObj = Object.fromEntries(fruits);
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JavaScript Object fromEntries() is supported in all browsers since January 2020:

Chrome 73 Edge 79 Firefox 63 Safari 12.1 Opera 60
Mar 2019 Jan 2020 Oct 2018 Mar 2019 Apr 2019


Optional catch Binding

From ES2019 you can omit the catch parameter if you don't need it:.

Example

Before 2019:

try {
// code
} catch (err) {
// code
}

After 2019:

try {
// code
} catch {
// code
}

Optional catch binding is supported in all browsers since January 2020:

Chrome 66 Edge 79 Firefox 58 Safari 11.1 Opera 53
Apr 2018 Jan 2020 Jan 2018 Mar 2018 May 2018

JavaScript Array flat()

ES2019 added the Array flat() method to JavaScript.

The flat() method creates a new array by flattening a nested array.

Example

const myArr = [[1,2],[3,4],[5,6]];
const newArr = myArr.flat();
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JavaScript Array flat() is supported in all browsers since January 2020:

Chrome 69 Edge 79 Firefox 62 Safari 12 Opera 56
Sep 2018 Jan 2020 Sep 2018 Sep 2018 Sep 2018

JavaScript Array flatMap()

ES2019 added the Array flatMap() method to JavaScript.

The flatMap() method first maps all elements of an Array and then creates a new array by flattening the array.

Example

const myArr = [1, 2, 3, 4, 5,6];
const newArr = myArr.flatMap((x) => x * 2);
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JavaScript Array flatMap() is supported in all browsers since January 2020:

Chrome 69 Edge 79 Firefox 62 Safari 12 Opera 56
Sep 2018 Jan 2020 Sep 2018 Sep 2018 Sep 2018

Stable Array sort()

ES2019 revised the Array sort() method.

Before 2019, the specification allowed unstable sorting algorithms such as QuickSort.

After ES2019, browsers must use a stable sorting algorithm:

When sorting elements on a value, the elements must keep their relative position to other elements with the same value.

Example

const myArr = [
  {name:"X00",price:100 },
  {name:"X01",price:100 },
  {name:"X02",price:100 },
  {name:"X03",price:100 },
  {name:"X04",price:110 },
  {name:"X05",price:110 },
  {name:"X06",price:110 },
  {name:"X07",price:110 }
];
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In the example above, when sorting on price, the result is not allowed to come out with the names in an other relelative position like like this:

X01 100
X03 100
X00 100
X03 100
X05 110
X04 110
X06 110
X07 110

Revised JSON.stringify()

ES2019 revised the JSON stringify() method.

Before 2019, JSON could not stringify character encoded with \.

Example

let text = JSON.stringify("\u26D4");
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Before ES2019, using JSON.stringify()JSON on UTF-8 code points (U+D800 to U+DFFF) returned broken Unicode characters like ���.

After this revision, strings with UTF-8 code points convert safely with JSON.stringify(), and back to the original using JSON.parse().


Separator Symbols

Line separators and paragraph separator symbols (\u2028 and \u2029) are now allowed in string literals.

Before 2019, these were treated as line terminators and resulted in error exceptions:

Example

// This is valid in ES2019:
let text = "\u2028";
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Note

Now, JavaScript and JSON have equal rules.

Before ES2019:

text = JSON.parse('"\u2028"') would parse to ''.

text = '"\u2028"' would give syntax error.


Revised Function toString()

ES2019 revised the Function toString() method.

The toString() method returns a string representing the source code of a function.

From 2019, toString() must return the source code of the function including comments, spaces, and syntax details.

Before 2019, different browsers returned different variants of the function (like without comments and spaces). From 2019 the function should be returned exactly as it is written.

Example

function myFunction(p1, p2) {
  return p1 * p2;
}
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