Summary  
This chapter introduces the ES6 spread operator to unpack elements from one array into another and to expand an array into individual function arguments, demonstrating how element order depends on the spread placement and how to print the results.

General domain of usage  
Array manipulation

The spread operator (`…`) can be easily used to assign an array's values to another array. 

let arr = [5, 6, 7, 8, 9];
let numbers = [1, 2, 3, 4, ...arr];
console.log (numbers);

Changing the position of the`...arr` term will change the position of data in the output:

let arr = [5, 6, 7, 8, 9];
let numbers = [1, 2, ...arr, 3, 4];
console.log (numbers);

The spread operator `…` unpacks the array `arr` elements and places them at the location. This can be used in many flexible ways, like passing arguments to a function:

let values = [1, 7, 9];
function sum(a, b, c) {
    return a + b + c;
}
console.log (sum(...values));

## Task

Complete the following code by creating a new array called `numbers` and append the elements of both `even` and `odd` arrays (in this order) to the `numbers` array. Do it in a single line of code.

In this course, we will learn how to use the JavaScript React library for making front-end applications. This course will help you understand the structure of a React application, how to add it to an existing website, and how to set up a React app from scratch. You will learn how to easily create React applications and expand them further for more advanced purposes. This course is intended for beginners though basic knowledge of JavaScript is required.

In this section we will explore why React is useful and why it is worth learning it at all. We will also learn one prerequisite, ES6, which will be used throughout the course.

In this section, we will learn another prerequisite - JSX which will be used throughout the course. Finally, we will explore some example code to get acquainted with React.

In this section we will learn about the essential and practical parts of React excluding the components – which will be covered in the next section. We will look at how JSX can be used with React, and how to create and render more complex elements in the React DOM using JSX. We will also learn how to set up a React based project, and we will explore its structure for deepening our understanding.

In this section you’ll be introduced to React components. We will look at what React components are and why we need them. We will explore the two different types of React components and learn the syntax for creating them. We will use them to create a single page application that displays X.

In this section we will learn more about how to combine JavaScript and JSX to create dynamic content. We will also learn how to pass data between components. In the end we will also explore event handling.

In the end of the previous chapter, we tried making a Todo application though in our attempt to do so we soon discovered that we needed some method for re-rendering the components once the data is updated in a component as React wasn’t automatically doing that for us. In this section we will learn how to fix such issues using ‘Hooks’. We will learn and implement hooks in detail. By the end of this section, you will be able to create stateful components in React and combine them to create complex web applications.

In this chapter we will learn how to add different pages to our React application and render different components based on URL. You will gain sufficient knowledge to be able to create multi-page applications.

ES6 Spread Operator

Task