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:
 Number : integer or decimal (like 5 7 2.35 ...)
 String : (like "car", "house", "tree" ...)
 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
 "+" addition operator Adds two values
 " " subtraction operator Subtracts two values
 "*" multiplication operator Multiplies two values
 "/" division operator Divides two values
 "=" 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.
 "+ =" add two values and store the result in the variable (on the left)
 "  = " subtracts two values and stores the result in the variable
 "* = " multiplies two values and stores the result in the variable
 " / =" divide two values and store the result in the variable
2  3  Comparison Operators


Example given x=7;


2  4  Logical operators&& which means AND operator : implies that all conditions are fulfilled 
