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A variable is simply a place or more like a container that hold information.
We need to label the information with a descriptive name, so our program could be understood more clearly by the reader. we can modify, replace or delete the information in a variable by its name.
To create(define or declare) a variable, use
when we assign or store the information, we use the
let firstName; firstName = "Deepak"; // store the string
we use camelCase while naming the variable
In single line, we can declare and assign a value to a variable
let firstName = "Deepak";
we can also declare multiple variables at once in a single statement
let firstName = "Deepak", lastName = "Kumar"; // multiple assignments
You can use any unicode character in a variable name. You can even use emoji as variable name 🎉
let \u1f60b1 = "iPhone";
It is not recommended to use emoji as identifier
We can also copy data from one variable to another
let firstName = "Deepak"; let firstName2 = "Suriya"; firstName = firstName2;
- Variables must be identified with unique names.
- Names can contain letters, digits, underscores, and dollar signs.
- Reserved like
letcan not be used as variable name.
- Variable names are case sensitive.
country and Country are different variables
- Variable names must begin with letters.
- Variable names can also begin with $ and _.
let $ = 4; // 4 let _ = $ + 1; // 5
Variable declared with
let can be changed or reassigned later. Sometimes you don't want your variable to be changed like PORT number of your server. Once
const is initialized, its value can never be changed again. An attempt to do so would cause an error.
const PORT = 1313; // declare a constant
constants are named using capital letters and underscores.
const IP_ADDRESS = '127.0.0.1'; const WHITE_COLOR = '#ffffff';
Constants can also used as aliases for difficult to remember values like color codes.
var also declares a variable like
let. You can find the
var in old scripts.
var score = 10;
var is slightly different from
let. We will cover the differences later.