জাভাস্ক্রিপ্টে ভেরিয়েবল এবং ডেটা টাইপ

Variables

• In JavaScript, a variable is a container that holds a value.
• Variables are declared using the let, const, or var keywords.
• let and const are block-scoped, while var is function-scoped.
• const variables cannot be reassigned, while let and var variables can be reassigned.

Data Types

• Primitive Data Types:
  • Number (e.g., 1, 3.14)
  • String (e.g., "hello", 'hello')
  • Boolean (e.g., true, false)
  • Null (e.g., null)
  • Undefined (e.g., undefined)
• Complex Data Types:
  • Array (e.g., [1, 2, 3])
  • Object (e.g., {name: "John", age: 30})

Functions

• A function is a block of code that can be executed multiple times from different parts of a program.
• Functions can take arguments, which are values passed to the function when it is called.
• Functions can return values, which can be used by the calling code.
• Functions can be declared using the function keyword or as an arrow function (e.g., () => { ... }).

Conditional Statements

• If Statement:
  • Used to execute a block of code if a condition is true.
  • Syntax: if (condition) { code to execute }
• If-Else Statement:
  • Used to execute a block of code if a condition is true, and another block of code if the condition is false.
  • Syntax: if (condition) { code to execute } else { code to execute }
• Switch Statement:
  • Used to execute a block of code based on the value of an expression.
  • Syntax: switch (expression) { case value: code to execute; break; ... }

Loops

• For Loop:
  • Used to execute a block of code repeatedly for a specified number of iterations.
  • Syntax: for (initialization; condition; increment) { code to execute }
• While Loop:
  • Used to execute a block of code repeatedly while a condition is true.
  • Syntax: while (condition) { code to execute }
• Do-While Loop:
  • Used to execute a block of code repeatedly while a condition is true.
  • Syntax: do { code to execute } while (condition)
• For-Of Loop:
  • Used to execute a block of code for each item in an iterable (e.g., array, string).
  • Syntax: for (variable of iterable) { code to execute }