function.js

// function is a block of reusable code that performs a specific task or calculates a value
// function doesn't have a name it's called anonymous function

// Function Declarations
function fnName() { console.log("fnName") }
fnName();

const fnName1 = function () { console.log("fnName1") }
fnName1();

// with parameters
function fnName2(params) { console.log(params) }
fnName2("kalidas");  // "kalidas" is argument

// return function
function sum(x, y) { return x + y }
console.log(sum(1, 2)); // 3

// default Parameter
function calc(x, y = 10) { return x + y }
console.log(calc(5, 5)) // 10
console.log(calc(5)) // 15

// rest Parameter
// Is something that allows a fn to accept any number of arguments
// only one rest parameter in fn and rest parameter must be last
function display(params, ...restParams) {
    console.log(params)
    console.log(restParams)
}
display("hi", "kalidas", "software developer");

// arrow function or fat arrow syntax
// arrow fun not binding this keyword
const sub = (x, y) => x - y;
console.log(sub(10, 5));



// closure function
/* a closure is a combination of a function and the lexical 
environment within which that function was declared. This means
that a closure has access to variables and parameters of its outer function even 
after the outer function has finished executing */
// or nested fn is a closure

function outer(x) {
    function inner(y) {
        return x + y
    }
    return inner;
}

const outerFn = outer(10);
console.log(outerFn(5)) // 10

// callback function
/* A callback function in JavaScript is a function that is passed as an argument to 
another function and is executed after some asynchronous operation,
Callback functions are commonly used in event handling, AJAX requests, 
and asynchronous programming */

function doSomethingAsync(callback) {
    setTimeout(function () {
        console.log("Async operation completed");
        callback();
    }, 2000);
}

function callbackFunction() {
    console.log("Callback function executed");
}

doSomethingAsync(callbackFunction);

// high order function (HOF)
// HOF is a function, it's take one or more fn as argument and it may return fn
// map, filter, reduce are HOF's
function returnFn() {
    return function () {
        console.log("inner fn")
    }
}

const fn = returnFn();
fn();

// pure function
// is a fn it's produce same output as a input
function welcome(name) {
    console.log(`Hi ${name}`)
}
welcome("kalidas");

// im pure function
// is a fn it's not produce same output as a input

let msg = "hai";
function welcome1(name) {
    console.log(`${msg} ${name}`)
}
welcome1("kalidas"); // hai kalidas
msg = "welcome";
welcome1("kalidas"); // welcome kalidas

// IIFE (Immediately Invoked Function Expression)
(function () {
    console.log("IIFE fn")
})();

// recursion
// fn that refer or call itself with base condition

/* function fn(){ 
    if(condition) return
    console.log("---fn---")
    fn();
 }
fn() 

const f1=function f2(){
    if(condition) return
    f1()
}
f1()
*/

function fetchWater(count){
    if(count===0){
        console.log("no more water")
        return 
    }
    console.log("fetching water...")
    fetchWater(count-1)
}
fetchWater(4);