===========================JAVASCRIPT=======================
INTRODUCTION :
JavaScript (js) is a light-weight object-oriented programming language which is used by several
websites for scripting the webpages. It is an interpreted, full-fledged programming language that
enables dynamic interactivity on websites when applied to an HTML document. It was introduced
in the year 1995 for adding programs to the webpages in the Netscape Navigator browser.
1- What is JavaScript in explain?
What is JavaScript ? JavaScript is a dynamic computer programming language. It is lightweight and
most commonly used as a part of web pages, whose implementations allow client-side script to
interact with the user and make dynamic pages. It is an interpreted programming language with
object-oriented capabilities.
JavaScript is an asynchronous and concurrent programming language that offers a lot of flexibility.
2- JAVASCRIPT STATEMENT :-
JavaScript statements are composed of:
Values, Operators, Expressions, Keywords, and Comments.
Example: document.getElementById("demo").innerHTML = "Hello Dolly.";
3- The JavaScript syntax defines two types of values:
Fixed values
Variable values
Fixed values are called Literals.
Variable values are called Variables.
Literals :
3.1. Numbers are written with or without decimals:
Example- 10.50
1001
3.2. Strings are text, written within double or single quotes:
Example- "John Doe"
'John Doe'
Variables :
Using var - We can redeclare and reassign.
var x= 30;
var x= 20;
Using let - We can not redeclare but reassign.
let x =30;
x=20;
Using const - We can not redeclare and reassign.
const = 30;
variables are used to store data values, it's case sensitive.
A JavaScript variable declaration’s name must begin with:
A letter (A-Z or a-z)
A dollar sign ($)
Or an underscore (_)
Historically, programmers have used different ways of joining multiple words into one variable name:
Hyphens:
first-name, last-name, master-card, inter-city.
Note:-Hyphens are not allowed in JavaScript. They are reserved for subtractions.
Underscore:
first_name, last_name, master_card, inter_city.
Upper Camel Case (Pascal Case):
FirstName, LastName, MasterCard, InterCity.
Lower Camel Case:
JavaScript programmers tend to use camel case that starts with a lowercase letter:
firstName, lastName, masterCard, interCity.
4-Comment :
Conment is not executable statement in programming language there are
two type of programming language.
4.1 - Single line comment start with // -
// Not Excecutable statment
4.2 – Multiple line comment start with /* code... */-
/* Not Excecutable statment*/
5 – What is Tokens : Smallest unit/ Element of program call token.
Like : c = a + b;
There are a,=,a, +,b is smallest element of program.
5.1 – Constant : Constants are those who value never can be changes.
5.2 – Keyword : Keyword are those word which meaning already defined in compilers. Is is also called
RESERVE WORD.
Like : strings, numbers, booleans, undefined, and null.
5.3 – Identifier : It will identify variable, datatype, class,interface,function.
Like : let a; var c = a-b, const a1;
5.4 – Datatype : Datatype are those which is define storage for memory allocation.
JavaScript has 8 Datatypes
1. String
2. Number
3. Bigint
4. Boolean
5. Undefined
6. Null
7. Symbol
8. Object
The Object Datatype
The object data type can contain:
1. An object
2. An array
3. A date
5.5 – Operators : Operator are those which is perform the operation between operant.
Like: The Addition Operator + adds numbers:
The Assignment Operator = assigns a value to a variable.
Let X =6
Let Y =4
X +Y= Z
The Assignment Operator (=) assigns a value to a variable:
Let Z = 10;
Types of JavaScript Operators
Arithmetic Operators :
Example :
let a = 3;
let x = (100 + 50) * a;
Assignment Operators :
The Addition Assignment Operator (+=) adds a value to a variable.
Example
x= 10;
x += 5;
Comparison Operators :
Example :
let a1 =11;
let b2 =14;
let result = a< b;
String Operators :
Example:
let text1 = "A";
let text2 = "B";
let result = text1 < text2;
The + can also be used to add (concatenate) strings:
let text1 = "John";
let text2 = "Doe";
let text3 = text1 + " " + text2;
Logical Operators :
A typical arithmetic operation operates on two numbers.there are +,-,*,/,%,increments,decrements;
The two numbers can be literals:
let x = 100 + 50;
Incrementing
The increment operator (++) increments numbers. & The Decrement operator (--) increments numbers
let x = 5;
x++; , x--;
let z = x;
Bitwise Operators :
Ternary Operators :
Like : a>b ? True : False
6- Conditional Statements :
Very often when you write code, you want to perform different actions for different decisions.
You can use conditional statements in your code to do this.
In JavaScript we have the following conditional statements:
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
Use switch to specify many alternative blocks of code to be executed
6.1- if (condition) {
// block of code to be executed if the condition is true
}
6.2- if (condition) {
// block of code to be executed if the condition is true
} else {
// block of code to be executed if the condition is false
}
6.3- if (condition1) {
// block of code to be executed if condition1 is true
} else if (condition2) {
// block of code to be executed if the condition1 is false and condition2 is true
} else {
// block of code to be executed if the condition1 is false and condition2 is false
}
6.4-switch(expression) {
case x:
// code block
break;
case y:
// code block
break;
default:
// code block
}
7- Loop statements : loop statements are specify the range of program.
JavaScript supports different kinds of loops:
for - loops through a block of code a number of times
foreach -
while - loops through a block of code while a specified condition is true
do/while - also loops through a block of code while a specified condition is true
The for statement creates a loop with 3 optional expressions:
for (initialization 1; condition 2 ; increment/decrement 4) {
// 3 Execute block of code
}
for (let i =0; i <5; i++) {
text += "The number is " + i +"<br>";
}
The while loop is use to controll loop. This statement firstly check the condition given with while(). If
condition is true will execute block of code.
while (i < 10) {
text += "The number is " + i;
i++;
}
The Do while loop is also use to controll loop. This statement will be execute unconditionaly once and then
codition will check.
let i = 0;
do {
text += "The number is " + i;
i++;
}
while (i < 10);
The forEach method calls a function for each element in an array.
The forEach() method is not executed for empty elements.
<script>
let text = "";
const fruits = ["apple", "orange", "cherry"];
fruits.forEach(myFunction);
function myFunction(item, index) {
text += index + ": " + item + "<br>";
}
</script>
7.1- What is Object Declaration and Definition:
7.2- Array print with For loop and ForEach loop:
7.3- Array print with ForEach loop:
8- What is Arrow Function:
Arrow functions are us to write shorter function syntax:
Before Arrow:
hello = function() {
return "Hello World!";
}
With Arrow Function:
hello = () => {
return "Hello World!";
}
JavaScript Asynchronous
9- What is Callback Function:
A Callback function is function that is passed an argument to another function.
// function
function greet(name, callback) {
console.log('Hi' + ' ' + name);
callback();
}
// callback function
function callMe() {
console.log('I am callback function');
}
// passing function as an argument
greet('Peter', callMe);
Note : callMe function belong to key callback parameter.
10- JavaScript Promise and Promise Chaining:
In JavaScript, a promise is a good way to handle asynchronous operations. It is used to find out if the
asynchronous operation is successfully completed or not.
A promise may have one of three states.
i- Pending
ii- Fulfilled
iii- Rejected
A promise starts in a pending state. That means the process is not complete. If the operation is successful, the
process ends in a fulfilled state. And, if an error occurs, the process ends in a rejected state.
For example, when you request data from the server by using a promise, it will be in a pending state. When
the data arrives successfully, it will be in a fulfilled state. If an error occurs, then it will be in a rejected state.
Create a Promise
To create a promise object, we use the Promise() constructor.
let promise = new Promise(function(resolve, reject){
//do something
});
The Promise() constructor takes a function as an argument. The function also accepts two functions resolve()
and reject().
If the promise returns successfully, the resolve() function is called. And, if an error occurs, the reject()
function is called.
Example 1: Program with a Promise
const count = true;
let countValue = new Promise(function (resolve, reject) {
if (count) {
resolve("There is a count value.");
} else {
reject("There is no count value");
}
});
console.log(countValue);
11- Javscript async/await :
In this tutorial, you will learn about JavaScript async/await keywords with the help of examples.
We use the async keyword with a function to represent that the function is an asynchronous function. The
async function returns a promise.
The syntax of async function is:
async function name(parameter1, parameter2, ...paramaterN) {
// statements
}
Here,
name - name of the function
parameters - parameters that are passed to the function
JavaScript await Keyword -
The await keyword is used inside the async function to wait for the asynchronous operation.
let result = await promise;
The use of await pauses the async function until the promise returns a result (resolve or reject) value. For
example,
=============Quick Revise Practise Code :===========
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