1.What is JavaScript?
JavaScript is a scripting programing language used to make website interactive.
example: click a button -> something happens.
used with
Html for make Content Structue.
Css for to make Design and Style.
JS for to make a Behaviour.
2.what is Interpreter?
Interpreter is a program thats reads and executes a program line by line instead of execute whole program at once.Js also called Interpreter
programming language because its executes a program line by line.
Advantage: Error shown instantly.
Execute line by line.
Disadvantage: Slower than Compiler.
3.What is Variable In JavaScript and How to use?
Variable are declared a keyword like var , let and const.
example: var a=10;
let a=20;
let name="gunalan";
const a=true;
4.What is the Difference between Var Let and Const?
In JavaScript, variables are declared using three keywords: var, let, and const.
Each has different behavior in terms of scope, reusability, and mutability.
1.var is the oldest way to declare variables in JavaScript.
var name = "Guna";
Features:
Function-scoped (not block-scoped)
Can be allow redeclared
Can be reinitialized
Gets hoisted (moved to top internally)
var x = 10;
var x = 20; //its allowed
var is not recommended in modern development due to unexpected behavior.
example:
{
var a=10;
console.log(a);
}
output:10
---------------------
{
var a=10;
}
console.log(a);
output:10
2.let is used for variables that may change.But cant to redeclare. And its only access inside the block. Because its block-scope.
let a=10;
let a=15; //cant allow redeclare
a=15;//allow to reinitial.
Features:
Block-scoped ({ })
Can be updated
Cannot be redeclared in the same scope
example:
{
let a=10;
console.log(a);
}
output:10
---------------------
{
let a=10;
}
console.log(a);
output:a is not defined
3.const is used for values that should not change.
const age = 23;
Features:
Block-scoped
Cannot be updated
Cannot be redeclared
Must be initialized during declaration
example:
{
const a=10
console.log(a)
}
output:10
--------------------------
{
const a=10
}
console.log(a)
output:a is not defined.
