Declare Variables

<div id="codeeditor1-template"> <script> let text; </script> </div> <div id="codeeditor2-template"> <script> let text; text = "Hello World"; // Stores Hello World string data in text variable </script> </div> <div id="codeeditor3-template"> <script> let text = "Hello World"; // Stores Hello World string data in text variable document.write(text ); </script> </div> <div id="codeeditor4-template"> <script> let text = "Hello World"; // Stores Hello World string data in text variable text = "Welcome to our World"; // This will ignore the current value and assign the new variable data as "Welcome to our World" document.write(text ); </script> </div> <div id="codeeditor5-template"> <script> let text1 = "Hello World1", text2 = "Hello World1" </script> </div> <div id="codeeditor6-template"> <script> let text1 = "Hello World1" let text2 = "Hello World1" </script> </div> <div id="codeeditor7-template"> <script> const text1 = "Hello World1" </script> </div> <div id="codeeditor8-template"> <script> const text = "Hello World1" text = "Hello World2" // This line would fail and throw exception </script> </div> <div id="codeeditor9-template"> <script> var text1 = "Hello World1" text = "Welcome to our World"; // This will ignore the current value and assign the new variable data as "Welcome to our World" document.write(text1 ); </script> </div> <div id="codeeditor10-template"> <script> if(1==1){ var text1 = "Hello World1"; } document.write(text1 ); </script> </div> <div id="codeeditor11-template"> <script> if(1==1){ let text1 = "Hello World1"; } document.write(text1 ); // This will fail as let creates the variable in the same or above level block </script> </div> <div id="codeeditor12-template"> <script> var message1 = "Hello World1"; function function1(){ var message2 = "JavaScript!"; document.write(message1 + message2); //can access global and local variable } function1(); document.write(message1);//can access global variable document.write(message2); //error: can't access local variable </script> </div>

Declare Variables

A variable stores the data value that can be changed later on.

The following reserved keyword can be used to declare a variable

Using let

The following example creates the variable with the default value as null

CODE1

Using "=" operator allows us to assign value to our variable

CODE2

On the following example last assignment will be the value of the variable.

CODE3

We can also make the variable creation and assignment in single liner

CODE4

Multiple variables could be defined in a single line by using comma (,) charachter

CODE5

Although it can be defined in a single, to read code better we suggest to use multiple line on variable creation

CODE6
Using const

To create the variable with const keyword would make it unchangable.

CODE7

Second line of the following code would fail as the variable defined with const keyword which makes it unchangable.

CODE8
Using var

var keyword is very similiar to let keyword. The only difference is var has no block scope

CODE9

This will work as var creates the variable dynamicly when it executes the line

CODE10

This will fail as let creates the variable in the same or above level block

CODE11

On the following code function1 can access the global variable message1 and local variable message2. The last line will fail as message2 is part of function1 local variable

CODE12

1. Introduction

2. Fundamentals

Comment Your JavaScript Code
Declare Variables
Data Types
Type Conversions
+ Plus Operator
- Minus Operator
* Multiply Operator
* Multiply Operator (1)
% Modulus (Division Remainder) Operator
** Exponentiation Operator
Bitwise operators
Comparisons
Logical Operators
Interaction: alert, prompt, confirm, console.log
The "switch" statement
Loops: while, do while and for

3. Classes

4. Basic Syntax

5. Useful Codes

6. Web Components

Declare Variables

Using let

Using const

Using var

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