Javascript

Source: Dev.to

What is JavaScript?

Key concepts

• Interpreted
• Dynamical
• Scripting
• Object oriented
• Variables declaration

Variable declarations

let

let age = 30;
age = 31; // This is allowed

const

const pi = 3.14;

var

var count = 5;
var count = 10; // This is allowed

Rules for identifiers of variables

• Valid characters: letters, numbers, underscores (_), and dollar signs ($). Numbers cannot be the first character.
• Case‑sensitive: myVariable is different from myvariable.
• Reserved words: Keywords such as if, for, function, etc., cannot be used as variable names.

Data types

Primitive types

1. Number – numeric values (integers and decimals).
2. String – text enclosed in single or double quotes.
3. Boolean – logical value (true or false).
4. Undefined – a declared variable without an assigned value.

   // Output: undefined

5. Null – intentional absence of any value.

   let empty = null;

6. Symbol – unique and immutable values, often used as object keys.

   let sym = Symbol('unique');

7. BigInt – integers larger than Number.MAX_SAFE_INTEGER.

   let bigNumber = 123456789012345678901234567890n;

Non‑primitive datatypes

Non‑primitive types are objects and can store collections of data or more complex entities.

1. Object – key‑value pairs.

   let obj = {
       // properties go here
   };

2. Array – ordered list of values.

   let a = ["red", "green", "blue"];

3. Function – reusable blocks of code.

   function fun() {
       // function body
   }

Exploring JavaScript datatypes and variables: understanding common expressions

console.log(null === undefined);

• Expression: null === undefined
• Result: false