Variables & Javascript operators

1 - Javascript variables

1 - 1 Definition:

A Javascript variable is a container, ie it is introduced to represent or schematize a memory area or in other words an information storage location.

1 - 2 Types of Javascript variable:

Javascript includes 4 types of variables:

1. Number      :   integer or decimal (like 5 7 2.35 ...)
2. String         :   (like "car", "house", "tree" ...)
3. Booleans    :  (logical value such as true or false)

To declare a variable just put the var statement followed by the name of the variable

Example :

var x=5;
//we have just defined a variable x whose value is 5

Javascript is a dynamically typed language, which means that you do not have to declare the type of the variable. let's take the following example to clear up the trick:

var x = 5;
// the type of variable x is now numeric
x = "car";
// the language automatically convert 
//the type of the numeric variable to the string type

1 -3 Concaténation de variables

Le terme concaténation signifie : juxtaposition ou  enchaînement, et ici en javascript le terme veut dire mettre une variable juste à coté de l’autre, pour concaténer deux variables on utilise le symbol  « + » :

Exemple :

var x = "auto";
var y = "bus";
var z = x + y;
// the variable z takes "autobus" as value

<script language = "javascript">
var x = 5;
window.document.write ("the value of x is" + x);
// the symbol + here plays the role of concatenation
</ Script>

What will display after execution:

(it is a concatenation between a variable of numeric type x = 5 and a variable of type string "the value of x is: ")

2 - Javascript operators

An operator is a symbol used to manipulate variables, that is to say, to perform and evaluate operations ... There are several types of operators: arithmetic operators, assignment operators, comparison operators, logical operators ...

2 - 1 Arithmetic operators

Calculation operators allow to mathematically modify the value of a variable

1.   "+"   addition operator Adds two values
2.  " -"    subtraction operator Subtracts two values
3.   "*"   multiplication operator Multiplies two values
4.   "/"   division operator Divides two values
5.   "="  assignment operator Assigns a value to a variable x = 3 Put the value 3 in the variable x

2 - 2 Assignment Operators

These operators simplify operations such as adding a value to a variable and storing the result in the variable. For example: x = x + 2

With the assignment operators it is possible to write this operation in the following form: x + = 2. That is, if x = 3 it becomes after the operation 5.

1.  "+  ="  add two values ​​and store the result in the variable (on the left)
2. " -  = " subtracts two values ​​and stores the result in the variable
3.  "*  = " multiplies two values ​​and stores the result in the variable 
4. " / =" divide two values ​​and store the result in the variable

2 - 3 - Comparison Operators