Question

can any one explain me variables in java script.

Answer 1

Answer:

Variables

Most of the time, a JavaScript application needs to work with information. Here are two examples:

An online shop – the information might include goods being sold and a shopping cart.

A chat application – the information might include users, messages, and much more.

Variables are used to store this information.

A variable

A variable is a “named storage” for data. We can use variables to store goodies, visitors, and other data.

To create a variable in JavaScript, use the let keyword.

The statement below creates (in other words: declares) a variable with the name “message”:

let message;

Now, we can put some data into it by using the assignment operator =:

let message; message = 'Hello'; // store the string

The string is now saved into the memory area associated with the variable. We can access it using the variable name:

let message; message = 'Hello!'; alert(message); // shows the variable content

To be concise, we can combine the variable declaration and assignment into a single line:

let message = 'Hello!'; // define the variable and assign the value alert(message); // Hello!

We can also declare multiple variables in one line:

let user = 'John', age = 25, message = 'Hello';

That might seem shorter, but we don’t recommend it. For the sake of better readability, please use a single line per variable.

The multiline variant is a bit longer, but easier to read:

let user = 'John'; let age = 25; let message = 'Hello';

Some people also define multiple variables in this multiline style:

let user = 'John', age = 25, message = 'Hello';

…Or even in the “comma-first” style:

let user = 'John' , age = 25 , message = 'Hello';

Technically, all these variants do the same thing. So, it’s a matter of personal taste and aesthetics.

var instead of let

In older scripts, you may also find another keyword: var instead of let:

var message = 'Hello';

The var keyword is almost the same as let. It also declares a variable, but in a slightly different, “old-school” way.

There are subtle differences between let and var, but they do not matter for us yet. We’ll cover them in detail in the chapter The old "var".