ES2020: Summary of new features & examples 🔥

In this article, we’re going to review some of the latest and greatest features coming with ES2020. 🔥

🤠 Getting started

We are going to test these features in a Node.js environment using Babel.

Method #1: creating a project from scratch

Start by creating a new project:

$ mkdir es2020-tests
$ yarn init

Now add @babel/cli @babel/core @babel/node @babel/preset-env dependencies:

$ yarn add --dev @babel/cli @babel/core @babel/node @babel/preset-env

Create a .babelrc file:

{
    "presets": ["@babel/preset-env"]
}

Method #2: clone the source code repository

You can also clone the following GitHub repository that includes the setup and source code of the examples in this article.

$ git clone [e-mail]:olivierloverde/es2020-examples.git
$ yarn install

🤖 The ES2020 features

Private variable in Class

You can now declare a private variable in a class by using a hastag #. If a private variable is called outside of its class It will throw a SyntaxError.

class MyClass {
    #privateVariable = "Hello private world"

    helloWorld() { console.info(this.#privateVariable) }
}

const myClass = new MyClass()
myClass.helloWorld() // works
console.info(myClass.#privateVariable) // SyntaxError: Private field '#privateVariable' must be declared in an enclosing class

Source on GitHub

BigInt

There was a limitation on largest possible integer because of how Javascript represented number internally (it is using a 64-bit floating point, see IEE 754.

const maxInteger = Number.MAX_SAFE_INTEGER;

console.info(maxInteger); // 9007199254740991
console.info(maxInteger + 1); // 9007199254740992
console.info(maxInteger + 2); // 9007199254740992 ??
console.info(maxInteger + 3); // 9007199254740994
console.info(maxInteger + 200); // 9007199254741192 ??
console.info(maxInteger * 200); // 1801439850948198100 ??

Source on GitHub

Now there is a native solution, BigInt is a built-in object that provides a way to represent whole numbers larger than 2⁵³ — 1, which is the largest number in JS number).

You can create a BigInt by:

• creating a BigInt object: const value = BigInt(500)
• appending a n to a number: const value = 500n

For the moment, it cannot be used with methods in the built-in Math object and cannot be operated with Number. Bitwise operators are supported except >>> because all BigInts are signed.

// Using BigInt
const maxIntegerBigInt = BigInt(maxInteger);
console.info(maxIntegerBigInt); // 9007199254740991n
console.info(maxIntegerBigInt + 1n); // 9007199254740992n
console.info(maxIntegerBigInt + 2n); // 9007199254740993n 
console.info(maxIntegerBigInt + 3n); // 9007199254740994n 
console.info(maxIntegerBigInt + 200n); // 9007199254741191n
console.info(maxIntegerBigInt * 200n); // 1801439850948198200n

Source on GitHub

Promise.allSettled()

Promise.allSettled takes an array of Promise object as argument and waits that all promises settle to return the corresponding result as an array of objects {status, ?value, ?reason}.

const resolvingPromise1000ms = new Promise((resolve, reject) => setTimeout(resolve, 1000));
const rejectingPromise2000ms = new Promise((resolve, reject) => setTimeout(reject, 2000));

const timeCheckpoint = Date.now();
Promise.allSettled([
    resolvingPromise1000ms, 
    rejectingPromise2000ms
]).then(data => {
    const elapsedTimeInMS = Date.now() - timeCheckpoint;
    console.info(`Promise.allSettled resolved after ${elapsedTimeInMS}ms`)
    console.info(data)
});

/*
Promise.allSettled resolved after 2006ms // ? not sure why we have 6ms
[
  { status: 'fulfilled', value: undefined },
  { status: 'rejected', reason: undefined }
]
*/

Source on GitHub

Nullish Coalescing Operator

When you use || operator, it returns the first argument to be true. However, sometimes you a default value considered as false such as 0 or "". To avoid it we can use the nullish coalescing operator ?? like below:

let object = {
    car: {
        speed: 0,
        name: ""
    }
};

console.info(object.car.speed || 90); // 90
console.info(object.car.speed ?? 90); // 0

console.info(null || true); // true
console.info(null ?? true); // true

console.info(undefined || true); // true
console.info(undefined ?? true); // true

console.info(0 || true); // true
console.info(0 ?? true); // 0

console.info("" || true); // true
console.info("" ?? true); // ""

console.info([] || true); // []
console.info([] ?? true); // []

console.info({} || true); // {}
console.info({} ?? true); // {}

console.info(true || "hey"); // true
console.info(true ?? "hey"); // true

console.info(false || true); // true
console.info(false ?? true); // false

Source on GitHub

Optional Chaining Operator

Let's take the following object as an example:

let person = {
    name: "John",
    age: 20
};

Let's say we want to access a property on this object that we are not sure to have, we usually do:

if (person.city !== undefined &&  person.city.locale !== undefined) {
    const cityLocale =  person.city.locale;
}

This ensures the program does not throw any "error cannot read property name of undefined".

Now with the optional chaining operator, we can be more concise:

console.info(person?.city?.locale);

Source on GitHub

Dynamic Import

Dynamic import() returns a promise for the module namespace object of the requested module. Thus, we can now use the import() function with the await keyword and assign the module namespace object to a variable dynamically.

const print = (value) => console.info(value);

export { print };

Source on GitHub

const doPrint = async (value) => {
    const Print = await import('./print.js');

    Print.print(value)
};

doPrint('Dynamic import works !');

Source on GitHub

String.prototype.matchAll

String.prototype.match gives an array of all matches between a string and a regexp.

For example:

const re = /(Mister )\w+/g;
const str = 'Mister Smith with Mister Galladon';
const matches = str.matchAll(re);

console.info(matches); // Object [RegExp String Iterator] {}
console.info(Array.from(matches));
/*
[
  [
    'Mister Smith',
    'Mister ',
    index: 0,
    input: 'Mister Smith with Mister Galladon',
    groups: undefined
  ],
  [
    'Mister Galladon',
    'Mister ',
    index: 18,
    input: 'Mister Smith with Mister Galladon',
    groups: undefined
  ]
]
*/

Source on GitHub

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You are now ready to use these new ES2020 features! Please leave me comment if you've liked it! 🙌

---

This article was originally posted on my blog olivier.codes - https://olivier.codes/2020/04/12/ES2020-Summary-of-new-features-with-examples/

Comments

[Mihail Malo]

creating a BigInt object: const value = new BigInt(500)

That's the same as new String() and new Number(), in the sense that people shouldn't do this.
The example below correctly does const value = BigInt(maxInteger), a conversion call like Boolean(Number('0')).
But the description uses new, pls fix.

[Olivier]

Good catch ! You are correct, we should not use new with BigInt. I've updated the article accordingly. Thank you!

[Chathula Sampath]

Thanks for share! Useful information 😍

[Gentian Shkembi]

On the first example you are accessing an undefined instance property, it should be myClass.#privateVariable instead of myClass.#helloWorld

[Olivier]

Thanks very much for catching this typo! I've updated the article and the source code accordingly. 🤠

[Gentian Shkembi]

You're welcome :)