ES2020: Summary of new features & examples 🔥
Olivier
Posted on April 12, 2020
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 git@github.com: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
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 ??
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
BigIntobject:const value = BigInt(500) - appending a
nto 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
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 }
]
*/
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
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);
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 };
const doPrint = async (value) => {
const Print = await import('./print.js');
Print.print(value)
};
doPrint('Dynamic import works !');
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
]
]
*/
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/
Posted on April 12, 2020
Join Our Newsletter. No Spam, Only the good stuff.
Sign up to receive the latest update from our blog.
Related