⚡ Java Script history and basics ⚡

🟡 Javascript History

1. JS first name was Mocha (coffee)
2. It was introduced by Netscape Browser.
3. Since, microsoft introduced Internet Explorer with it's own script and different for Netscape so it was difficulty for developers.
4. To Solve this issue, ECMA came.
5. ES6 is different types of versions introduced by ECMA.

🟡 Basics

🟠 Data Types

🔴 Primitve Data Type (Single value)

1. Number: 7,1.616, 45.22
2. String: Any Characters kept inside a double or single quote are called a String. Ex: "Shobham" , "2" , "1.235","45%"
3. Boolean: By John Boole Ex: 0 and 1
4. Empty Values: null, undefined

🔴 Non-Primitive Data Type (Multiple values also called Objects)

1. Array: Collection of values written inside [] and separated by ", "| which can be of the same or different data type.

   Ex: [1,2,3,4,5] , ["Ram","Shyam","Shobham"], [[1,2,3],["Ram","Shyam"]

   Array Index: The position of elements inside the Array is called by Index.

   Ex: [1,2,3,4,"Ram"] Here the position of "Ram" is index 4. Index starts from 0.

   Note: Syntax: Set of instructions used to run the js program.

2. Object: Elements inside {} and in the form of key-value pairs are called Objects.

   Ex: {abc:"LCO"}

🟠 Variables

Variables are the container that holds the value which might be a number, string, boolean, or anything. Variables are important because, without them, our tasks will be tedious. We have to use our given input again and again to perform the task.

Let's create a variable.

Step:1 Declaration We will use the let keyword to declare the variable.

let yourName;
let yourAge;

Currently, they don't have values, they are empty containers. Let's store the value inside them.

Step:2 Initialize After declaring the variable name, initialize it to give some value.

yourName= "Rohan";
yourAge=25;

We can declare and initialize the variables together like this.

let myName= "Prateek";
let myAge= 25;

🔴 Different ways to declare the variables

Using var keyword

var userName= "Sam";

When js came into the picture, the var keyword was mostly used, but due to its confusing nature, let and const came into the picture.

Using let keyword

let userAge= 56;

You can't redeclare the variable again once declared by let. Try in your console.

let userAge= 89;
let userAge= 25;
// Throws error

And this is a good thing for throwing errors to avoid confusion, but in var, you can declare as much as you can. That's why I always use let and const.

With let, you can update your variable.

userAge= 54;

There is also a naming convention to declare the variables. I will suggest you read naming convention article.

Using const keyword As per the name, it is used when to want to make something constant.

const user; // error
const user= 25; // correct

You can not declare and initialize using const separately, it needs to be done together.

🔴 Variables Types

1. Numbers You can store integers, decimals, floating, and doubles inside variables.

    let num1= 25;
    let num2= 2.53;
   

2. Strings Anything inside a double or single quote is called a string.

    let yourName= "Pratyush";
    let youAge= "25";
   

3. Boolean It returns true or false.

    let isNum= 5>2;
    console.log(isNum); // true
   

   Note: To print your variables in the console, you can use this syntax in the editor. console.log(your variable name);

4. Arrays Arrays in js are the container that stores multiple elements with the same or different data types inside [] and these elements are separated by a comma.

    let array1= [1,2,3,4,5];
   

   To access the elements, we use the array index which starts from 0.

    console.log(array1[0]); // 1
   

5. Objects

      let person = {
      name:"Prateek",
        age:25
        }