var var1 = 10; // local variable 
var2 = 10; //global var2
let var3 = 10; // block statements scope
const number=42; // block statements scope, can't be changed.

// for-each
var arr = [10, 25, 7, 100, 20]; // initialise arr
// iterate array from start to end
arr.forEach(x => console.log(x));

// for-in
var obj = {'one': 1, 'two': 2, 'three': 3}; // initialise an object
 
for(var i in obj){
    console.log("key:",i, "value:",obj[i]); // print key and value
}

function sumFunc(a, b) {
    return a+b;
}
 
// anonymous function
var var1 = 5; // assign 5 to var1
var var2 = 6; // assign 6 to var2
var var3 = function (a , b){
    console.log('Taking sum in the function'); // print to see function execute
    var ans = a + b; // assign sum of a and b to ans
    return ans; // return ans as output
}
console.log(var3(var1, var2)); // print the value of var3
 
 
// Invoke functions at their declaration#
var var3 = function (a , b){
    console.log('Taking sum in the function'); // print to see function execute
    var ans = a + b; // assign sum of a and b to ans
    return ans; // return ans as output
}(var1, var2); // invoke the function
 
// arrow functions/fat arrow function / anonymous functions
var func = (a, b) => { // Create arrow function for taking sum of two numbers
    var sum = a + b; // take sum of a and b and assign to sum variable
    return sum; // return sum
}
 
// single-lined function
var func = (a, b) => a + b; // arrow function assigned to func to add a and b
console.log("Sum of 1 and 3:" , func(1,3)); // print func with arguments 1 and 3 
 
// single argument arrow function
var func = a  => a * 2; // func assigned to arrow function which doubles argument a
 
// arrow function without arguments.
var func =  () => console.log("Hello"); // arrow function that prints hello
 
// passing a function as an argument
function foo (func){ // Create function taking another function as argument
    console.log("in foo function");
    console.log("calling func");
    func(); // invoke the function passed as argument
    console.log("finished calling");
    console.log("returning");
}
 
foo(() => console.log("Hello")); // invoke foo and pass printHello as argument

// forEach
var arr = [10, 20, 30, 40, 50]; // initialise an array and assign to arr
arr.forEach((val, ind, array) => { 
    // arrow function to print arguments (value, index, array)
    console.log("Value:", val, " Index:", ind, " arr:",array); // print values
    });
console.log(arr); // print array assigned to arr
 
// two arguments: (val, ind) =>
// one argument: (val) =>
 
// filter
var arr = [10, 20, 30, 40, 50]; // initialise an array and assign to arr
var arr1 = arr.filter(a => a > 30); // Filter elements greater than 30
 
// find
var arr = [10, 20, 30, 40, 50]; // initialise an array and assign to arr
var val = arr.find(a => a > 20); // find an element greater than 20

// map function to modify each elements
var arr = [10, 20, 30, 40, 50]; // initialise an array and assign to arr
var arr1 = arr.map(a => a * 2); // double the element in the array
 
// reduce function to reduces the array to a single value from left to right.
function callbackfn(prev: any, curr: any, index: number, array: number[])
// This callbackfn function takes from 2 to 4 arguments. 
var arr = [10, 20, 30, 40, 50]; // initialise an array and assign to arr
var val = arr.reduce((prev, curr) => prev + curr); // reduce element to sum
 
// Using the map and reduce methods to count elements
var arr = ['Hello', 1, true, NaN, 'Bye']; // initialise an array of elements
var countArr = arr.map(ele => typeof ele === 'string' ? 1 : 0); // map to 0 and 1
var sum = countArr.reduce((prev, curr)=> prev + curr); // reduce for sum
console.log("arr:",arr); // print original array
console.log("array from map:", countArr); // print array returned from map method
console.log("number of Strings:",sum); // print number of strings 
 
var sum = arr.map(ele => (typeof ele === 'string' ? 1 : 0) // map to 0 and 1
    ).reduce((prev, curr)=> prev + curr); // reduce to find sum
console.log("arr:",arr); // print original array
console.log("number of Strings:",sum); // print number of strings