JAVASCRIPT

 JS COMMENTS

     *It is most important in java script.

    *It is used to explain the java script code.

 Single line comments

   * Single line comments start with //. 

   *Any text between // and the end of the line will be ignored by JavaScript.

          Example

     let x = 5;      // Declare x, give it the value of 5

  Multiple line comments 

    *Multi-line comments start with /* and end with */.

     *Any text between /* and */ will be ignored by JavaScript.

              Example 

           /*
                   The code below will change
                   the heading with id = "myAnbu"
                   and the paragraph with id = "myAnbu"
                    */

Variables

     * Variables are containers for storing data   

          Example 

          var x = 5;
                var y = 6;
                var z = x+  y;

       In this example, x, y, and z, are variables, declared with the let keyword: 

 Operators

 assignment operator 

   *The assignment operator (=) assigns a value to a variable. 

              Example  

           let c = 10;

   addition operator 

    *The addition operator (+) adds numbers: 

                   Example  

          let x = 5;
          let y = 2;
          let z =  x + y;
          document.getElementById("demo").innerHTML = z;    

  String operator

     To add

                      let text1 = "John";
                      let text2 = "Doe";
                      let text3 = text1 + " " + text2;
                      document.getElementById("demo").innerHTML = text3;
                      Output
                      John Doe

   Logical operator

       &&  AND gate

    || OR gate

      ! NOT gate

 AND gate

*It is the strict gate, It will pass only whether the 2 statement is pass

0  && 0 = 0

0 && 1 = 0

1 && 0 =0

1 && 1 = 1

OR gate

* It will pass whether the 1 statement is pass

0 || 0 = 0

0 || 1 = 1

1 || 0 = 1

1 || 1 = 1  

Examples

        x=4;
         y=7;
        (x > 2 &&  y < 5 )

         *  In this line we want to see whether the two condition   is right.

         *  First we saw x is greater than 2 and  y is smaller than 5.

         * In this case x is greater than 2 and y is not less than 5, So it is false.

Datatypes

Strings

(let doll = "It's alright";)

Numbers

Let x=2;

 Boolean

      Booleans can only have two values: true or false.

let x = 5;
let y = 5;
let z = 6;
(x == y)       // Returns true
(x == z)       // Returns false

 Array

      If you have a list of items , storing the cars in single variables.

         if you want to loop through the cars and find a specific one? And what     

  if you had not 3 cars, but 300?

         The solution is an array!

        An array can hold many values under a single name, and you can  

access the values by referring to an index number.

 Example

const cars = ["Tata", "Volvo", "BMW"];
console.log( cars[0]);
Output
Tata

  Object

     In real life, a car is an object.

        A car has properties like weight and colour, and methods like start and    stop:

        All cars have the same properties, but the property values differ from car to car.

             const person = {
                             firstName: "John",
                             lastName: "Doe",
                              age: 50,
                              eyeColor: "blue"
                                                                 };
 
                       document.getElementById("demo").innerHTML =
                   person.firstName + " is " + person.age + " years old.";
                 Output
                   John is 50 years old.

 Functions

       A JavaScript function is a block of code designed to perform a particular task.

A JavaScript function is executed when "something" invokes it (calls it).

Example

function myFunction(p1, p2) {
  return p1 * p2;
}
document.getElementById("demo").innerHTML = myFunction(4, 3);
Output
12    

 If/Else

Conditional statements are used to perform different actions based on different conditions.

Use if to specify a block of code to be executed, if a specified condition is true

Use else to specify a block of code to be executed, if the same condition is false

Use else if to specify a new condition to test, if the first condition is false

Example

Const hour=20
if (hour < 18) {
  greeting = "Good day";
} else {
  greeting = "Good evening";
}
 
console.log( greeting);
Output
 
Good evening

Switch

     * The value of the expression is compared with the values of each case.

    * If there is a match, the associated block of code is executed.

    * If there is no match, the default code block is executed.

Example

const day = "Monday";
switch (day) {
  case "Monday":
    console.log("Have fun");
    break;
  case "Tuesday":
    console.log("Going to job");
    break;
  case "Wednesday":
    console.log("playing carrom");
    break;
  case "Thursday":
    console.log("playing chess");
    break;
  case "Friday":
    console.log("Watching movies");
    break;
default:
console.log("nothing else to say");
}

    For loop

loops through a block of code a number of times.

Statement 1: sets a variable before the loop starts (let i = 0).

Statement 2 : defines the condition for the loop to run (i must be less than 5).

Statement 3 : increases a value (i++) each time the code block in the loop has been executed.

Example

let symbols = ["*", "**", "***", "****", "*****"];
for (let i = 0; i< 5; i++) {
  console.log(symbols[i]);
}
  Output
 *
 **
 ***
  ****

Map

*We set the value of the key in a map

*We get the value of a key in a map

   Example

     const fruits = new Map([
  ["apples", 500],
  ["bananas", 300],
  ["oranges", 200]
]);
 
document.getElementById("demo").innerHTML = fruits.get("apples");
 Output
 500