Slide 1

WHAT IS JAVASCRIPT VARIABLES?

A variable is a container for a value, like a number we might use in a sum, or a string that we might use as part of a sentence. But one special thing about variables is that their contained values can change. Let's look at a simple example:

Example:- Click Here

In this example pressing the button runs a couple of lines of code. The first line pops a box up on the screen that asks the reader to enter their name, and then stores the value in a variable. The second line displays a welcome message that includes their name, taken from the variable value.

Slide 2

To understand why this is so useful, let's think about how we'd write this example without using a variable. It would end up looking something like this:

 let name = prompt('What is your name?');

 if (name === 'Adam') {
   alert('Hello Adam, nice to see you!');
 } else if (name === 'Alan') {
   alert('Hello Alan, nice to see you!');
 } else if (name === 'Bella') {
   alert('Hello Bella, nice to see you!');
 } else if (name === 'Bianca') {
   alert('Hello Bianca, nice to see you!');
 } else if (name === 'Chris') {
   alert('Hello Chris, nice to see you!');
 }
 // ... and so on ...

Slide 3

You may not fully understand the syntax we are using (yet!), but you should be able to get the idea — if we didn't have variables available, we'd have to implement a giant code block that checked what the entered name was, and then display the appropriate message for any name. This is obviously really inefficient (the code is a lot bigger, even for only five choices), and it just wouldn't work — you couldn't possibly store all possible choices.

Variables just make sense, and as you learn more about JavaScript they will start to become second nature.

Slide 4

Another special thing about variables is that they can contain just about anything — not just strings and numbers. Variables can also contain complex data and even entire functions to do amazing things. You'll learn more about this as you go along.

Note: We say variables contain values. This is an important distinction to make. Variables aren't the values themselves; they are containers for values. You can think of them being like little cardboard boxes that you can store things in.

Ref:- https://developer.mozilla.org/en-US/docs/Learn/JavaScript/First_steps/Variables