JavaScript: Variables

What are variables?

We use variables to store data values. For example, we can use variables to store a user’s email address or name. In JavaScript, a variable can contain any type of data, such as a string, a true or false boolean, an object, or a number.

Variable Declaration

The variable declaration means creating a variable.

There are 3 ways to declare a variable, using keywords:

// var (a.k.a. VARIABLE)
var name;

// let
let age;

// const (a.k.a. CONSTANT)
const isMale;

Variable Assignment

Variable assignment means assigning a value to the variable you declared.

We use the = symbol to do a variable assignment.

// 1. Declaring variables.
var name;
let age;

// 2. Assign values to the variables we declared.
name = 'Yap';
age = 20;

Notice we didn't show an example of using const. This is because const has a different way of using it. We will show this in the next section.

Variable Initialization

Variable initialization means we declare and assign the value at the same time.

var name = 'Yap';
let age = 20;
const isMale = true; // this is how you use `const`

To understand more why we can't declare and assign separately with const. Continue on reading...

Variable Reassignment

Variable reassignment means we change the value of a variable to something else.

But, we can't reassign if the variable is declared by using const. Because const means constant (a.k.a. value that doesn't change). Hence, we can only initialize a const variable because it cannot do an assignment.

var name = 'Yap';
console.log(name); // output: Yap

name = 'Kaiz';
console.log(name); // output: Kaiz (changed!)
let age = 20;
console.log(age); // output: 20

age = 30;
console.log(age); // output: 30 (changed!)
const isMale = true;
console.log(isMale); // output: true

isMale = false; // TypeError: Assignment to constant variable.

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