Next-Generation Javascript | Modern Javascript  Refresher

Next-Generation Javascript | Modern Javascript Refresher

Rahul Dubey's photo
Rahul Dubey
·Jan 10, 2022·

6 min read

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In this article, I provided a brief introduction to some core next-gen JavaScript features, of course focusing on the ones you'll see the most in this courseHere's a quick summary!

let & const

Read more about let : developer.mozilla.org/en-US docs/Web/JavaScript/Reference/Statements/let Read more about const : developer.mozilla.org/en-US/docs/Web/JavaSc..

let and const basically replace var You use let instead of var and const instead of var if you plan on never re-assigning this "variable" (effectively turning it into a constant therefore).

ES6 Arrow Functions

Read more: developer.mozilla.org/en-US/docs/Web/JavaSc..

Arrow functions are a different way of creating functions in JavaScriptBesides a shorter syntax, they offer advantages when it comes to keeping the scope of the this keyword (see here).

Arrow function syntax may look strange but it's actually simple.

 function callMe(name) { 
    console.log(name);
 }

which you could also write as:

 const callMe = function(name) { 
    console.log(name);
 }

becomes:

 const callMe = (name) => { 
    console.log(name);
 }

Important:

When having no arguments, you have to use empty parentheses in the function declaration:

 const callMe = () => { 
    console.log('Max!');
 }

When having exactly one argument, you may omit the parentheses:

 const callMe = name => { 
    console.log(name);
 }

When just returning a value, you can use the following shortcut:

 const returnMe = name => name

That's equal to:

const returnMe = name => { 
    return name;
 }

Exports & Imports

In React projects (and actually in all modern JavaScript projects), you split your code across multiple JavaScript files - so-called modulesYou do this, to keep each file/ module focused and manageable.

To still access functionality in another file, you need export (to make it available) and import (to get access) statements.

You got two different types of exports: default (unnamed) and named exports:

default => export default ...;

named => export const someData = ...;

You can import default exports like this:

import someNameOfYourChoice from './path/to/file.js';

Surprisingly, someNameOfYourChoice is totally up to you. Named exports have to be imported by their name:

import { someData } from './path/to/file.js';

A file can only contain one default and an unlimited amount of named exportsYou can also mix the one default with any amount of named exports in one and the same file. When importing named exports, you can also import all named exports at once with the following syntax:

import * as upToYou from './path/to/file.js';

upToYou is - well - up to you and simply bundles all exported variables/functions in one JavaScript objectFor example, if you

export const someData = ..(/path/to/file.js )

you can access it on upToYou like this:

upToYou.someData

Classes

Classes are a feature which basically replace constructor functions and prototypesYou can define blueprints for JavaScript objects with them

Like this:

class Person {
    constructor () {
        this.name = 'Max';
    }
}

const person = new Person();
console.log(person.name); // prints 'Max'

In the above example, not only the class but also a property of that class (=> name ) is definedThey syntax you see there, is the "old" syntax for defining propertiesIn modern JavaScript projects (as the one used in this course), you can use the following, more convenient way of defining class properties:

class Person {
    name = 'Max';
}

const person = new Person();
console.log(person.name); // prints 'Max'

You can also define methodsEither like this:

class Person {
    name = 'Max';
    printMyName () {
    console.log(this.name); // this is required to refer to the class!
    }
}

const person = new Person();
person.printMyName();

Or like this:

class Person {
    name = 'Max';
    printMyName = () => {
    console.log(this.name);
    }
}

const person = new Person();
person.printMyName();

The second approach has the same advantage as all arrow functions have: The this keyword doesn't change its reference. You can also use inheritance when using classes:

class Human {
    species = 'human';
}
.
class Person extends Human {
    name = 'Max';
    printMyName = () => {
    console.log(this.name);
}
}
.
const person = new Person();
person.printMyName();
console.log(person.species); // prints 'human'

Spread & Rest Operator

The spread and rest operators actually use the same syntax:

..

Yes, that is the operator - just three dotsIt's usage determines whether you're using it as the spread or rest operator.

Using the Spread Operator:

The spread operator allows you to pull elements out of an array (=> split the array into a list of its elements) or pull the properties out of an objectHere are two examples:

const oldArray = [1, 2, 3];
const newArray = [...oldArray, 4, 5]; // This now is [1, 2, 3, 4, 5];

Here's the spread operator used on an object:

const oldObject = {
    name: 'Max'
};
const newObject = {
    ...oldObject,
    age: 28
};

newObject would then be

{
name: 'Max',
age: 28
}

The spread operator is extremely useful for cloning arrays and objectsSince both are reference types (and not primitives), copying them safely (i.epreventing future mutation of the copied original) can be trickyWith the spread operator you have an easy way of creating a (shallow!) clone of the object or array

Destructuring

Destructuring allows you to easily access the values of arrays or objects and assign them to variables. Here's an example for an array:

const array = [1, 2, 3];
const [a, b] = array;
console.log(a); // prints 1
console.log(b); // prints 2
console.log(array); // prints [1, 2, 3]

And here for an object:

const myObj = {
    name: 'Max',
    age: 28
}
const {name} = myObj;
console.log(name); // prints 'Max'
console.log(age); // prints undefined
console.log(myObj); // prints {name: 'Max', age: 28}

Destructuring is very useful when working with function argumentsConsider this example:

const printName = (personObj) => {
console.log(personObj.name);
}
printName({name: 'Max', age: 28}); // prints 'Max'

Here, we only want to print the name in the function but we pass a complete person object to the functionOf course this is no issue but it forces us to call personObj.name inside of our functionWe can condense this code with destructuring:

const printName = ({name}) => {
console.log(name);
}
printName({name: 'Max', age: 28}); // prints 'Max')

We get the same result as above but we save some code By destructuring, we simply pull out the name property and store it in a variable/ argument named name which we then can use in the function body.

JS Array Functions

Not really next-gen JavaScript, but also important: JavaScript array functions like map() , filter() , reduce() etc.

You'll see me use them quite a bit since a lot of React concepts rely on working with arrays (in immutable ways).

The following page gives a good overview over the various methods you can use on the array prototype - feel free to click through them and refresh your knowledge as required: developer.mozilla.org/en-US/docs/Web/JavaSc..

Particularly important in this course are:

map() => developer.mozilla.org/en-US/docs/Web/JavaSc..

find() => developer.mozilla.org/en-US/docs/Web/JavaSc..

findIndex() => developer.mozilla.org/en-US/docs/Web/JavaSc..

filter() => developer.mozilla.org/en-US/docs/Web/JavaSc..

reduce() => developer.mozilla.org/en-US/docs/Web/JavaSc..

concat() => developer.mozilla.org/en-US/docs/Web/JavaSc..

slice() => developer.mozilla.org/en-US/docs/Web/JavaSc..

splice() => developer.mozilla.org/en-US/docs/Web/JavaSc..

 
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