Variables and Data Types in Javascript

This is a study note about Javascript from https://www.geeksforgeeks.org/introduction-to-javascript-course-learn-how-to-build-a-task-tracker-using-javascript/

Javascript is untyped language. Once a variable is created in javascript using 'var', you can assign any other type of data to this variable.

var text = 'Hello World'

text = 123

Above code is valid in Javascript. Variable text can be assigned a string value and then later change to a number.

1. Difference between var and let in Javascript

Basically, 'var' is function scoped, however 'let' is block scoped.

https://www.geeksforgeeks.org/difference-between-var-and-let-in-javascript/

Let's use use 'let' for most of the cases because 'var' is confusing.

2. Number type in Javascript

The number type in Javascript contains both integer and floating point numbers. Besides these numbers, we also have 'special-numbers' in Javascript that are: 'infinity', '-Infinity' and 'NaN'. The 'NaN' denotes a computational error.

let num = 2; // integer

let num2 = 1.3; // floating point number

let num3 = Infinity; // Infinity

let num4 = 'something here too'/2; // NaN

3. String type in Javascript

There are three types of quotes in Javascript:

let str = "Hello There";

let str2 = 'Single quotes works fine';

let phrase = `can embed ${str}`;

There's no difference between 'single' and "double" quotes in Javascript. Backticks provide extra functionality as with the help of them we can embed variables inside them.

let variable = "Leo";

// embed a variable

alert( `Hello, ${variable}!` ); // Hello, Leo!

4, Undefined type in Javascript

The meaning of undefined is 'value is not assigned'.

let x;

console.log(x); // undefined

5, Object type in Javascript

Everything in Javascript is Object. There are two ways to create objects.

let person = new Object();

let person = {};

You can initialise object with properties like below:

let person = {

name: "Mukul",

age: 22,

}