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JS Variables


What are the variables?

Variables are just containers that store data values.

Just like a bag with some fruits.

They can be declared using the following reserved keywords

  • var
  • const
  • let

Skeleton of a JavaScript variable

var title = 'JavaScript Tutorial';

Use varkeyword to create a variable.

The title is the variable name that could be any such as i, first_name, lastName, etc.

The equals = operator assigns a value on the right to the variable on the left and it’s called an assignment operator. 

Finally, 'JavaScript Tutorial' is an actual data value which is String data type as it’s wrapped within single quotes.

In a nutshell, The title variable stores the string value ‘JavaScript Tutorial’

JavaScript Variable Rules

👉 Variable names can be a short name (a, b) or descriptive (title, first_name).

👉 They can be a combination of letters, numbers, underscores (_) & dollar signs ($).

👉 The first letter of a variable name can’t start with numbers.

👉 They are case sensitive and the title and Title are NOT the same variables.

👉 No reserver keywords can be used as a variable name such as var etc.

JavaScript Variable Declaration

var title = 'JavaScript Tutorial' ;

The title variable declared with an initial value ‘JavaScript Tutorial’.

var author;  // var author = undefined

The author variable declared without initial value will have a value of undefined

Re-assign JavaScript Variable

Re-assign a new value to the variable title without var keyword after initialization.

var title = 'JavaScript Tutorial' ;
title = 'The Best JavaScript Tutorial';

The value of the title will be preserved when creating a same variable without an initial value after it’s initialized.

var title = 'JavaScript Tutorial' ;
var title; // 'JavaScript Tutorial'

JavaScript Data Types

JavaScript variables can store many types such as number, string, etc.

The value of string type is just a text wrapped with single or double-quotes such as ‘Front-end Developer’, ‘HTML5 Tutorial’

The value of number type is a digit without quotes such as 100, 8.14, etc.

var title = 'JavaScript Tutorials'; // String type
var students = 1000; // Number type

A value of Number type inside quotes considered String type as well.

var students = '1000'; // String type NOT Number type

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