main.js

// PROBLEM 1: DOM
var btn1 = document.getElementById("btn1");
btn1.onclick = function() {
	document.getElementById("answer1").innerHTML = problem1();
};

// PROBLEM 1: FUNCTION
function problem1() {
	var max = document.getElementById('input1').value;
	var sum = 0;
	if (max === "") {
		return "Uoh-ooh, you forgot to specify a number!";
	}
	if(max > 10000) {
		return "Please specify a number between 0-10000";
	}
	for(var i = 1; i< max; i++){
		if(i % 3 === 0 || i % 5 === 0){
			sum += i;
		}
	}
	return sum;
}

// PROBLEM 2: DOM
var btn2 = document.getElementById("btn2");
btn2.onclick = function() {
	document.getElementById("answer2").innerHTML = problem2();
};

// PROBLEM 2: FUNCTION
function problem2() {
	var max = document.getElementById('input2').value;
	var x = 0;
	var y = 1;
	var sum;
	var total = 0;
	if (max === "") {
		return "Uoh-ooh, you forgot to specify a number!";
	}
	if(max > 5000000) {
		return "Please specify a number between 0-5000000";
	}
	for (sum=0; sum<max; sum=x+y) {
		if (sum%2 === 0) {
			total += sum;
		}
		x=y;
		y=sum;
	}
	return total;
}


// PROBLEM 3: DOM
var btn3 = document.getElementById("btn3");
btn3.onclick = function() {
	document.getElementById("answer3").innerHTML = problem3();
};

// PROBLEM 3: FUNCTION
function problem3() {
	var max = document.getElementById('input3').value;
	if (max === "") {
		return "Uoh-ooh, you forgot to specify a number!";
	}
	if(max > 5000000) {
		return "Please specify a number between 0-5000000";
	}
	for (var i=2; i<=max; i++) {
		if (!(max % i)) {
			max /= i;
			i--;
		}
	}
	return i;
}

// PROBLEM 4: DOM
var btn4 = document.getElementById("btn4");
btn4.onclick = function() {
	document.getElementById("answer4").innerHTML = problem4();
};

// PROBLEM 4: FUNCTION
function problem4() {
	var max = document.getElementById('input4').value;
	if (max === "") {
		return "Uoh-ooh, you forgot to specify both numbers!";
	}
	if(max > 5) {
		return "Please specify a number between 0-5";
	}
	var i, n, m, d, inf, sup, limit, number = 0;
	for (i = 1; i < max; i += 1) {
		number = 10 * number + 9;
	}
	inf = number;
	sup = 10 * number + 9;

	function isPalindromic(n) {
		var p = 0, q = n, r;
		while (n > 0) {
			r = n % 10;
			p = 10 * p + r;
			n = Math.floor(n / 10);
		}
		return p === q;
	}

	for (n = sup * sup, m = inf * inf; n > m; n -= 1) {
		if (isPalindromic(n)) {
			limit = Math.ceil(Math.sqrt(n));
			d = sup;
			while (d >= limit) {
				if (n % d === 0 && n / d > inf) {
					return n;
				}
				d -= 1;
			}
		}
	}
	return NaN;
}

// PROBLEM 5: DOM
var btn5 = document.getElementById("btn5");
btn5.onclick = function() {
	document.getElementById("answer5").innerHTML = problem5();
};

// PROBLEM 5: FUNCTION
function problem5() {
	var max = document.getElementById('input5').value;
	if (max === "") {
		return "Uoh-ooh, you forgot to specify a number!";
	}
	if(max > 100) {
		return "Please specify a number between 0-100";
	}


	var i, n = 1;

	function largestPower(n, max) {
		var p, e = 2, largest = n;
		while ((p = Math.pow(n, e)) <= max) {
			largest = p;
			e += 1;
		}
		return largest;
	}

	function isPrime(n) {
		var i, max = Math.ceil(Math.sqrt(n));
        // since the main loop generates odd numbers only
        // we can start testing primality dividing by 3
        for (i = 3; i <= max; i += 2) {
        	if (n % i === 0) {
        		return false;
        	}
        }
        return true;
    }

    for (i = 3; i <= max; i += 2) {
    	if (isPrime(i)) {
    		n *= largestPower(i, max);
    	}
    }

    return n * largestPower(2, max);
}