Reversed a string woo!

I feel like I've reversed a string before... I vaguely remember something about halving the length and swapping things around the middle. But this time, when Free Code Camp asked for it as their very first JavaScript coding exercise, I just looped through the entire thing. Woooo!

function reverseString(str) {
var reverseStr = '';
for (var i = str.length - 1; i > -1; i--){
reverseStr += str[i];
console.log(reverseStr);
}
return reverseStr;
}

reverseString('hello');

At first I had just defined the reverseString variable as "var reverseStr;", and the readout I was getting from that console.log in the loop was "NaNo" "NaNol" etc. Second debugging step, when I made the start point of the loop i = str.length - 1 instead of i = str.length, I got "undefinedo" "undefinedol" "undefinedoll" etc. So in the first case it was trying to add the nothing in "hello"[5] to NaN, since why, the sensible programming language thinks, would I be trying to use an addition operator, +, on anything but a number? I'm not sure why trying to add "o" worked; I suppose JavaScript decided that the o it was getting meant that it should be adding to a string or object or some non-number thing, but that string or object or whatever wasn't defined. It's nice that when it failed at adding it relapsed to concatenating.

...I suspect this is a terrible implementation of reversing a string. Any takers?

The Free Code Camp at this point suggests I should be pairing, and a nice guy in the chat room linked me up with a copy of Screenhero (they've joined Slack and are not taking new signups unless someone already inside invites you in), which they suggest is good for being able to remotely cowork and see everything on another screen... Another guy in the chat suggested coderpad.io or another .io solution instead, as less dangerous and better functioning. What do people think, re: screen sharing programs?

Free Code Camp Bonfire 4 and 5

So, 4 was trivial, which was great: make a function that factorializes numbers. Like, 5! is 1 * 2 * 3 * 4 * 5 = 120.

function factorialize(num) {
for (var i = (num - 1); i > 0; i--) {
num *= i;
}
return num;
}

factorialize(5);

But 5... I feel like I shouldn't have to make my own function that takes an array and jams it all into a single string without commas separating the bits. But the concat stuff I was looking at in the Mozilla Developer Network wasn't working that way (even though their example shows it should. So baffled).

And I feel like there must be some way to not declare like 7 variables... But I couldn't figure out how to chain these methods/functions. Anyway: here it is, a function that checks if a statement is a palindrome (ignoring all the non-letter things! The RegEx stuff was honestly fun learning).

function reverseString(str) {
var reverseStr = '';
for (var i = str.length - 1; i > -1; i--){
reverseStr += str[i];
}
return reverseStr;
}

function arrToRevStr(arr) {
var str = '';
for (var i = arr.length - 1; i > -1; i--){
str += arr[i];
}
return str;
}

function palindrome(str) {
var cleanStrArray = /(\w)/g.exec(str);
var cleanStr = arrToRevStr(cleanStrArray);
var cleanStrLow = cleanStr.toLowerCase();

var reverseStr = reverseString(str);
var cleanReverseStrArray = /(\w)/g.exec(reverseStr);
var cleanReverseStr = arrToRevStr(cleanReverseStrArray);
var cleanReverseStrLow = cleanReverseStr.toLowerCase();

if (cleanStrLow == cleanReverseStrLow) {return true;}
else {return false;}
}

palindrome("eye");