A large difference exists between a variable and a string-type literal (data types will be discussed later).

Assume you want to print the "**like**" word in the console. If you run the following command, you will get an error:

`ReferenceError` tells you that the variable `like` is not defined.

The interpreter looks for a variable, function, or keyword with the name `like`.

# Variable Structure

Variables in JS have some data: name, address to the cell in memory, data type, and value.

- **Name:** it's the name of a variable you give when defining it.

- **Memory address:** when a variable is created, a place in memory is allocated to store it.

- **Type:** this is a type of data the variable contains.

- **Value:** this is the data that the variable stores.

> Note
>
> **Literal** contains **Type** and **Value** too. The variable gets literal if you need to use it in a function, operator, or something else.

# Defining
To define a variable you need to use the `let` keyword and choose a **name** for this variable:

```javascript
let nameOfVariable;
```

> Note
>
> Variables should be named in **camelCase** style. The **camelCase** means that words are written together without a space, and each word (except the first) must be capitalized.

The new variable contains an `undefined` value by default.

- The `undefined` value means that nothing contains in a variable.

You can assign and reassign a value to the variable:

let numb;
numb = 100;

console.log(numb);

numb = 100 + 20;

console.log(numb);

# Usage
Variables are the main core of different programs. You can use every variable an unlimited number of times.

Consider a case when you write 1000 lines of code using literals but make a typo in one word that repeats not once... You need to correct each word in your code and lose more time.

Now, look at the example (but with less number of lines):

console.log("Hello Word!");
console.log("I love this Word!");
console.log("I need to live in this Word!");
console.log("This Word is the best!");

Here author lost the `l` letter in the `World` word. To fix this program you need to correct each line.

Look at the next example:

let x = "Word";

console.log("Hello " + x + "!");
console.log("I love this " + x + "!");
console.log("I need to live in this " + x + "!");
console.log("This " + x + " is the best!");

> Note
>
> In the example above, **string concatenation** is used. The **string concatenation** will be described in the next section.

First, let's get acquainted with JavaScript and look at its syntax. In this section, you will get a basic familiarity with the JavaScript syntax to make it easier to learn in detail later on.

Now it's time to learn about the data types that JavaScript works with. We'll start by looking at the difference between literals and variables, and then delve into the various data types.

We have become familiar with the various data types. Now, let's learn how to work with them by learning the operations we can perform with each data type.

Next, we will learn how to control the flow of execution. It's a straightforward process: we can tell the interpreter exactly what to do under certain conditions.

Next, we will explore how to shorten code using repetitive looped actions. We will examine the types of loops available in JavaScript and learn how to work with them.

Finally, to be able to write simple programs, we need to learn about functions that can make our lives much easier. We will learn how to create and use our functions.