09_function.js

//Function Declaration / defining 
//Block of code that performs a specific task , can be invoked whenever needed.Function saves from redundancy means repeating 
// Function Definition & Function Call or Invoke

//Declaring Functions

//Simple Declaration
function see(fishes) {
    return `we have ${fishes} fish`;
}
;
//Declaring function and Holding in a variable
let addnums = function (num) {
    return num + 2;
};

//
function myFunction(msg) {
    console.log(msg);
}
myFunction("I love JS"); // arguments
// Function to Calculate Sum & return
// Imp is that function parameters -> like local variable -> Block scope of function
function sumFunction(a, b) {
    let s = a + b;
    return s; // returns are last to right else what ever written after will definetly not run
}
let val = sumFunction(3, 4);
console.log(val);

// OPTIONAL PARAMETERS in Functions / parameterized function
function disp_details(id, name, mail_id) {
    console.log("ID:", id);
    console.log("Name", name);
    if (mail_id != undefined) // The function prints the value of mail_id only if the argument is passed a value.
        console.log("Email Id", mail_id); //If an optional parameter is not passed a value during the function call, the parameter’s value is set to undefined
}
disp_details(123, "John");
disp_details(111, "mary", "mary@xyz.com");

//ARROW FUNCTION. Compact way of writing a Function , Arrow function stores its value in a variable.
// () => {} Syntax for Arrow Function
// () : number => {}
let arrowFunction = (x, y) => {
    let sum = x + y;
    return sum;
};
let vals = arrowFunction(8, 10);
console.log(vals);
//Arrow -2
let prepNewMeal = (dishName) => {
    console.log("Making:" + dishName);
};
prepNewMeal("Russian Salad");


//Calculate an Average bt 3 numbers with Arrow Function
let AvgFunction = (a, b, c) => {
    let avg = (a + b + c) / 3;
    return avg;
};
let result = AvgFunction(40, 20, 22);
console.log(result);

//Q: Function that takes a String as an argument and returns the number of Vowels in the string
function countVowels(word) {
    word = word.toLowerCase();
    let count = 0;
    for (let chr of word) {
        if (chr === "a" ||
            chr === "e" ||
            chr === "i" ||
            chr === "o" ||
            chr === "u") {
            count++;
        }
    }
    return count;
}
const inputWord = "Apna College";
const vowelCount = countVowels(inputWord);
console.log(`Number of vowels in "${inputWord}": ${vowelCount}`);
// Create an arrow funtion to perform same task
let countvowels = (word) => {
    word = word.toLowerCase();
    let count = 0;
    for (let chr of word) {
        if (chr === "a" ||
            chr === "e" ||
            chr === "i" ||
            chr === "o" ||
            chr === "u") {
            count++;
        }
    }
    return count;
};
const inputWords = "Apna College";
const vowelsCount = countVowels(inputWord);
console.log(`Number of vowels in "${inputWord}": ${vowelCount}`);


// Callback Function: In TS a function can be passed as an arguemnts to another funtion 
// for an array (only used for Arrays) forEach method is used by using call back funtion
// Interview Question: forEach is also called as Higher order function/ Method having parameters/n
// and return other function as output, where there is a call back function as paramter in another function it becomes a higher order function.
let arr1 = ["Islamabad", "lahore", "Karachi"];
arr1.forEach((val, idx, arr) => {
    console.log(val.toUpperCase(), idx, arr);
});
//Practice Question : for a given array , print squre of each value using forEach loop.
let arryNum = [1, 2, 3, 4, 5, 6];
arryNum.forEach((val) => {
    console.log(val * val);
});
// Or another way 
// let calSqure =(val) =>  {
//   console.log(val * val)
//  }
//  arryNum.forEach(calSqure);
function calculateAverage(num1, num2) {
    return (num1 + num2) / 2; // when this method return value its type will be number
}
let avg = calculateAverage(20, 50); //20 +50/2 =35
console.log(avg);

//same method with arrow Function
// let avg2 = (num1: number, num2: number) => (num1+num2)/2; 
let avg2 = (num1, num2) => {
    let myAvg = (num1 + num2) / 2;
    return myAvg;
};
// a Function which do not return a value 
function calculateAverage2() {
    console.log("Calculating Average");
}
// using this function in a variable to store a value
let avg3 = calculateAverage2();
console.log(avg3);
let f3 = (age, name) => {
    return `Mr .${name}, your age is ${age}`;
};
console.log(f3(100, "Aimon"));

//Optional Parameters
function optParmas(param1, param2 = "Gamma", param3 = 10) {
    console.log(`${param1}, ${param2}, ${param3}`);
    return `${param1}, ${param2}, ${param3}`;
}
let xyz = optParmas(10, "Alpha", 20); // if we set some varibale default at the end as above 
console.log(xyz);
let xyz2 = optParmas(10, "Beta"); //  if we call it this way what should print here
console.log(xyz2); // what would print here, printing two times as once in method and once we ourself printing
let xyz3 = optParmas(10); // where there is a no value and make that print it is rule of thum that underfined print there and first parameter can never be optional
console.log(xyz3);
// why first parameter can not be optional below
// before required paramter there could not be a optional paramter this is rule of thumb
function optParams2(num1, num2) {
    console.log(num1);
    console.log(num2);
}
//optParams2();
//optParams2(10);
optParams2(10, 20);
//Functions - and syntax:
// function fun_name(parameter) {
//code
// }
//function declaration
function greet(name) {
    console.log("Hello, " + name.toUpperCase() + "!!");
}
greet("John"); //function call
//function declaration
function Welcome(parameter) {
    console.log(`Welcome ${parameter}`);
}
Welcome("wania"); //function call
Welcome("Class 54");
function getFavoriteNumber() {
    return "Value is positive";
}
// console.log(getFavoriteNumber())
getFavoriteNumber();
//Arrow Function
let sum1 = (x, y) => {
    return x + y;
};
// console.log(sum1(2,3))
//Arrays
let arr = [1, 2, 3, 4, 5, 6];
console.log(arr[0]);
// how to return accurate
function addTwo(num) {
    return num + 2;
    //return "Hello" // this is a point of concern  , this can be avoided by adding a retuen type
}
let results = addTwo(5);
// returning more than one types, can be done by using union types
function getValue(myVal) {
    if (myVal > 5) {
        return true;
    }
    return "200 K";
}
function handlerr(errmsg) {
    throw new Error("this is an error");
}
export {};




/* Arrow functions: 
Arrow function and This Keyword, study about this further ahead regarding prototypal Inheritance
in future, this keyword tells about Current Context 
To understand arrow function   understand this  and to understand This. Have to go back to  Object. */


// Declaring Functions through Arrow Functions

const arrowFunc = () => {
    let user = "AmCucumb"
    console.log(this); // we get {} in return
}

() => { } //  basic arrow can also hold in a variable
const newArrow2 = (num1 , num2 ) => {
    return num1 + num2
}
newArrow2(2 ,5)


//Arrow Function is Also Used As an IMPLICIT RETURN

const arrowFour = (num1, num2) => num1 + num2
const arrowFour1 = (num1, num2) => (num1 + num2)

// returning an Object
const arrowFours = (num1, num2) => ({name : "amCucum"}) // we can return Objects like this


// V imp from react perspective when we use {} we have to write returnkeyword but incase of ( ) we cn omit return keywrd