Hello, my name is Vivek Chudasama, and I wrote this post about JS Basic Intro and History in my own words. So, I hope you enjoyed reading it.

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Intro to Javascript

Javascript is a high-level, multi-paradigm object-oriented scripting language. It is the world's most well-known and widely used programming language, earning it the moniker "Web programming language." It is used to program website functionality.

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A brief history of Javascript

• In 1995, Brendan Eich wrote the first version of Javascript, dubbed "Mocha," in just ten days.
• To attract Java developers, "Mocha" was renamed LiveScript, then Javascript in 1996. Javascript, on the other hand, has nothing to do with Java.
• When Microsoft introduced Internet Explorer, it included Netscape's Javascript and renamed it JScript.
• To standardize the language, ECMA published ECMAScript 1 (ES1), the first official JavaScript standard.
• ES5 was introduced with many exciting new features.
• ES6 was released: the most significant update to the language yet!
• ECMAScript switched to a yearly release cycle to ship fewer feature features every version.

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How to link Javascript to HTML?

• Go to your test site and create a Javascript file and name it script.js (or anything you want to) and save it.
• In your index.html file, enter this code on a new line, just before the closing tag:

    <script src="script.js"></script>

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First Javascript program

• Open the script.js file and type this line of code and save it.
• Open the test site and open the console (Ctrl + Shift + J or left click on the webpage and click on inspect, then open console.)
• Now, you can see the output there! Yay!!!

  console.log("Hello World!");
  

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Variables and Values

• The container for storing data is called a variable.
• The data stored in the variable is called a value.

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Declaring variables

As Javascript has dynamic typing, we do not have to manually define the data type of the value stored in the variable.

Syntax for declaration:

var variableName = value;
let variableName = value;
const variableName = value;

Things to keep in mind while naming a variable

• Only use alphanumerics, $, and _ for variable names.
• Never begin the name with a number and capital alphabet.
• Never use keywords like Name, Let, Switch, etc.
• As Javascript is case sensitive, do remember that variable names pen, pEN, and pEn would be considered different variables.

There are three ways to declare variables

• Var: It is used for all types of variables but is outdated.

  var firstName = "Vivek";
  

• Let: It is preferred over var for declaring variables. Let allows us change the value stored in it.

  let firstName = "Vivek";
  firstName = "Chudasama";
  

• Const: It is used to store values that can't be changed. Const doesn't allow us to change the value stored in it.

  const PI = 3.14 ;
  PI = aaplePI;  // This gives an error
  

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Datatypes

There are two types of datatypes :

1. Primitive
2. Non-Primitive

1. Primitive Datatypes

There are 7 primitive data types:

1. Number: Floating point numbers.

   let myNum = 3;
   

2. String: Collection of characters.

   let myName = "Vivek";
   

3. Boolean: Logical type that can be only true or false.

   let myBool = true;
   

4. Undefined: Value has been taken by a variable that isn't defined.

   let x;
   

5. Null: The empty value.
6. Symbol: Value that is unique and cannot be changed.
7. BigInt: Larger integers than the Number type can hold.

2. Non-Primitive Datatypes

1. Object: It contains various key: value pairs.

   const human = {
     firstName: "ABC";
     Lastname: "XYZ";
     age: x;
   }
   

   Template literals

   let firstName = "Vivek";
   let lastName = "Chudasama";
   let age = "23";
   

   To check the datatype of a variable, you can use typeof like given below

     let code = 2678;
     console.log(typeof num); // This would show "Number" in console
   

We all know the concatenation technique

          console.log("My name is + " " + firstName + " " + lastName and I'm + " " + age + years old.");
          // My name is Vivek Chudasama and I'm 23 years old.

Template literals involve the use of `...` instead of "..." and ${variable-name} is used instead on inserting empty quotation marks and + sign and makes code clean.

    console.log("My name is ${firstName} ${lastName} and I'm ${age} years old.");
    // My name is Vivek Chudasama and I'm 23 years old.

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Conditionals

In JavaScript we have the following conditional statements:

• if to specify a block of code to be executed if a specified condition is true.
• else to specify a block of code to be executed if the given condition is false.
• else if to specify a new condition to test if the first condition is false.

  let x = 5;    
  if(x == 3) {
    console.log("Three");
  } else if (x == 4) {
    console.log("Four");
  } else if (x == 5) {
    console.log("Five");
  } else {
    console.log("Not three, four or five");
  }
  

Switch Statement

• Switch statement is used to check various conditions. It is like a long ladder of if and else if except the actual usage.
• break is mandatory after each case. If the break is not used, the next block of code for the next case will be executed automatically. Syntax

  switch (expression) {
  case (expression output): 
    // Code
    break;
  case (expression output):
    // Code
    break;
  case (expression output): 
    // Code
    break;
  default: 
    // Code
  }