# Types, values, and variables in JavaScript

In this article, we will take an overview of types, values, and variables in JavaScript.

A compuer program can simply be explained as a piece of code that manipulates something.

So what is something?

Let’s ask the computer to perform some task,
*Hey, computer print “Hello Devs” 2 times.*

So, in the above statement, there are two **entities**,

1. “Hello Devs”
2. 2

These will be the **values **used by the computer program.
First is a set of characters and the second is digit/number these are called **types**.

Ok, what if we want these values later in our program?
Let’s save values in some container and name that container as **abc**.
This container is called a **variable**.

JavaScript types mainly can be divided into two categories:-

1. Primitive types
2. Object type

Primitive types include **numbers, strings of text,** and **boolean** values(true/false).
The special type of values like null and undefined are primitive values, but they are not numbers, strings, or boolean.
ES6 added a new special-purpose type, known as **Symbol**.

Any value that is not a primitive value(number, string, boolean, symbol, null, or undefined) is an **Object**.

An object is a collection of properties where each property has a name and value pair.
The values of an object can be a primitive value or another object.

> JavaScript automatically converts values from one type to another. If the program expects a string and you provided a number, it will automatically convert the number to a string.

## Numbers
The number is used to represent integers.
JavaScript represents numbers using a 64-bit floating-point format defined by IEEE 754 standard.

This means it can represent numbers as large as +/- 1.7976931348623157*10^308 and as small as +/- 5*10^-324.

If we use integer values larger than the range, we may lose precision in trailing digits.

If a number appears directly in a JavaScript program it is called **numeric literals**.
I will explain Numbers in detail in an upcoming article.

## Text
To represent text in our program JavaScript provides type as a String.<br>
A String is an immutable ordered sequence of 16-bit values. Each 16-bit value represents a Unicode character.<br>
The length is the number of 16-bit values that are used to represent a string.
JavaScript strings use zero-based indexing, the first 16-bit value is placed at 0th index and 2nd at 1st index, and so on.

You can find details about strings in javascript in upcoming articles.

## Boolean values
null is a reserved keyword to represent the absence of the value.<br>
Using typeof operator on null returns type as an “object”, indicating that null can be used as a special value that indicates “no object”.<br>
Other programming languages also have equivalent Javascript null: like NULL, nil, or None.

The undefined value represents a deeper kind of absence. It is the value of the variable that not has been initialized.<br>
Many times we see this value when we try to get the value of an object property or array element which does not exist.

**undefined is a predefined global constant(not language keyword as null) that is initialized to an undefined value.**

If we try to apply typeof operator to an undefined value it returns “undefined”, indicating that this is a member of a special type.

## Symbols
Symbols were introduced in ES6 to use non-string property names.<br>
JavaScript Object types are an unordered collection of properties, where each property has a name and value.<br>
Before ES6 property names are typically a **string**.

To obtain symbol values, we need to call the Symbol() function.
This function never returns the same value twice even we call it with the same argument.

**Symbol.for()-**
This method allows us to create the same symbol value twice.
Passing the same string argument to Symbol.for() method returns the same symbol value.
**Symbol.keyFor()** returns the string that we passed as an argument to **Symbol.for()**.

```
let var1 = Symbol.for(“test”);
let var2 = Symbol.for(“test”);
va1 === var2              // true
```

## Variable Declaration and Assignment
In the programming language, we use names/identifiers to represent values.<br>
Binding name to value gives us a way to refer to that value ad use it in the programs we write.<br>
By doing this we can say that we are assigning value to a variable.<be>

The term variable implies that a new value can be assigned: the value associated with the variable may vary as our program runs.<br>
If we permanently assign some value to a name, that name we refer to as constant instead of variable.

### Variable and scope
The scope of a variable is the region of our program source code in which it is defined.<br>
Variable and constant declared with let and const are blocked scope. This means the variable is only accessible inside the code block where let or const exists.

### var as a global variable
If we declare the global variable using the var keyword it is a part of the global object and can be referred to as globalThis.<br>
Global declared with var can not be deleted using the delete keyword.<br>
Variable declared with let and const are not a part of globalThis.<be>

This is an overview of Javascript types and variables.<br>
In the next article from this series, I will cover the Number data type in detail.

**Hope you like it, if yes \*\*like & share.\*\***

**Thanks for your time.**

**Happy coding….**

*
**[← How does JavaScript work? 🤔](https://blog.ganeshjaiwal.dev/how-does-javascript-work) [Numbers in JavaScript →](https://blog.ganeshjaiwal.dev/numbers-in-javascript)***