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All right.

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So let's go over the solutions to these three problems.

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Let's start with the first one is even so to get started here I'm going to go ahead and open up supply

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.

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I have an index that aged him I'll file and I'm going to add a script tag and we'll just call this solution

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that.

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Yes.

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So next up I need to make this solution that J file and I'm going to save that solution.

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Yes in the same place and quite safe.

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So again we're starting with is even.

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So I'm going to declare the function is even

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and it needs to take a single argument.

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Let's just call it numb and then we want to return true

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if even return false otherwise.

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So there's a few ways of doing this.

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The first one is to do it as explicitly as possible.

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So we're going to say if numb mod 2 is zero remember that's how we tell if something is even if the

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remainder of dividing two into that number is zero if there is no remainder.

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That means that it's even.

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So if that's the case we can return TRUE else return false.

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Just like that.

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And I'm going to move this up here

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just to make it clear what corresponds to what.

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Just like that.

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So we can do this.

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And I'm actually not going to call my function just yet.

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I'm going to open it up in the browser to show you something slightly new.

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So if I open up my console I actually have access to is even in my console here.

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So I type is even with no parentheses and it tells me yes I know about is even Here's the code and if

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I add the parentheses I need to pass that number in like 5 and I get false.

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And I can do it again with four or with one or with ninety nine and it works great.

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So there's two things there are is even works.

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So that's awesome.

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But more importantly I want to show you that we can define functions and code in our files.

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And then when we open those files up in the browser.

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In this case our aged him L5 that's connected to our javascript file.

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I can then access those functions.

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So there is a small refactor that we can make here.

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I'm going to copy this code commented all out and I'm going to shorten this up so I'm just going to

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show you the solution first and then we'll go over how it works.

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So this is substantially shorter return.

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Number two equals equals equals zero.

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So let's refresh the page.

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Make sure that it works is even for 4 is true is even if 3 is false.

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Still works the same way.

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So the way that it actually works this line here.

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Return Nahm made to triple equals zero.

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It's going to evaluate this first and that's a true or false statement it's a boolean statement.

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So numb to Tripoli equals zero is either going to be true or false.

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And then we're just returning true or false.

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So rather than checking if it's true return true and if it's false return false we just turn the value

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immediately.

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So that's a nice little shortcut there.

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So next up we have factorial.

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So I'm going to go ahead and start by defining my function called factorial function factorial and we

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know need to take a number.

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So down here I'm going to write a note.

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So if I did factorial of four that should give me four times three times two times one and I'm going

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to come with that.

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So inside of our function I'm going to write a few lines of pseudo code.

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The first thing that we know we want to do is define a result variable and then the very last thing

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in the function is return the result variable.

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So in-between that's important and that's where we're going to calculate

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factorial and store value in result.

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So we have a few approaches in how we can calculate factorial.

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We could either start by setting result to be one at the very beginning and then multiplying it by two

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and then multiplying it by three and then by 4 or we could go the other way around like we have here

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.

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And I'm going to start by doing it this way so you need to a result variable var result equals 1.

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And then what we need to do is multiply that result by every number between 1 and that number.

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So one in four or one in ten whatever is passed in as No.

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So to do that we'll want to use a loop we could use either a for loop or a while loop.

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I'm going to use a for loop here because it's a little bit shorter.

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So for far and let's just call it I.

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And we could start I as one.

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So I'll do that first.

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And we're going to keep multiplying while I is less than or equal to numb then we're going to add 1

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to i every time.

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And then all that we want to do is multiply result by I.

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So if we step through this if we did it for four factorial of four result starts as one right here then

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we're creating I start says 1 and we multiply result by.

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So that's just 1 times 1 which I noticed is unnecessary.

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So we might want to just start this at 2.

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So the first time through we multiply by times result.

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So we get 1 times 2.

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Next time through I is now three because we added one.

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So that is still less than the number which is four.

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So we multiply again result equals the current value a result which is this times 3.

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So then we have 6 and then the next time through I now is four.

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So four is less than or equal to four.

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That is true.

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So we're going to multiply one last time by four and then add one to I in our four loop and now we're

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done.

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Because now we're at 5 5.

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It's not less than or equal to four.

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So that's all we should need to do there.

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There's one small change we could make.

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We don't need to say result equals result times.

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I we can shorten this by using star equals which is just a shortcut for the exact same thing that we

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just had.

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And then the very last thing we need to do is return results.

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So save let's open it up in the browser refresh and we should have access to our factorial function

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.

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Let's try factorial of three and we get six.

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How about factorial of four or 10 which is 360 2000 or three million six hundred twenty eight thousand

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eight hundred which is what we got over here as the solution to factorial of 10.

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And then let's try it out.

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Factorial of zero.

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And we get one.

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So it works perfectly.

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So that's all we need to do factorial.

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As I mentioned you could do this in the other direction where we start with result equal to number.

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And we work backwards.

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And that would be a very simple modification.

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Basically we would change this to be numb and then we would start here at one below numb while I.

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Is greater than or equal to 1 i.

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Minus minus.

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So we're starting result is four and then we're going to multiply by 1 less than the result which is

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three and then subtract 1.

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So multiply by 2 and then multiply by 1 and then we're done.

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So that one definitely works as well.

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The only issue that we could run into if we refresh.

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Let's try this factorial of three.

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It gives us 6 5 gives us 120 and 0 gives us zero.

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So there is a problem there because when we started this way.

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Result is equal to numb.

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If we pass in zero we're starting result as zero.

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And then we're done.

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We're not multiplying 0 by anything.

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And even if we did it would still be zero.

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So the solution to that is we could have it simple if statement in here that could be something like

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if numb scores equals zero return 1.

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And remember if we have a return statement that short circuits everything.

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So now it should be good to go.

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However I prefer the first solution because it's shorter and we don't have to have that special case

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or that we need to do is set result equal to 1 at the beginning and that takes care of everything for

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us.

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All right so let's tackle the last one which is Khabab to snake.

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So remember this is supposed to take a single string and replace all the dashes with underscores.

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So it takes Khabab case turns it into Snake case.

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So I'm going to go define that function first and I'll just leave it empty to start.

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So function Let's make some space here.

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Function Khabab to snake takes in a single string.

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We'll just call it as TR and then we'll put our logic in there.

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But first I'm going to fill up some pseudo code again.

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What we want to do is replace all dashes with underscores

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and then lastly return as TR.

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So the crux of this problem is that we don't know how to actually do that.

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How do we replace all of one character in a string.

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And again that was deliberate.

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I wanted you to have to try and look this up to have to find this out on line.

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It is a really really important skill.

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So the first thing that I would do is figure out how I want to word my search on Google.

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So that sounds like something that would be pretty obvious but it really is going to have a big impact

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on the types of results that we get in the rule that I live by is that you want to make your search

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as general as possible so we don't want to include things about dashes and underscores or snake case

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and Khabab case.

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So instead we might want to make a search trying to find out how we replace any character in a string

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whether it's a dash or an underscore or a dollar sign.

160
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So let's go ahead and try that.

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I'm going to search for javascript replace character string.

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And let's see what we get.

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Get a few results here.

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I'd like to avoid W3 schools so let's try these two.

165
00:11:35,140 --> 00:11:37,740
How do I replace a character at a particular index.

166
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So that's not quite what we're looking for.

167
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This one looks good though.

168
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Replace all commas in a string.

169
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So because we didn't include the dash or the underscore the camel or kabab we got this result which

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will work just fine.

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This one is to replace all commas.

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We'll just need to change one tiny character in the solution rather than replacing commas.

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We want to replace dashes.

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So the way stack overflow works if you've never seen an up top is the askers question.

175
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So this is not where we want to read our solution.

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This is the asking of a question and answers are in reply.

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So under this answer section and here we go here's an answer.

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This person says you can use a regular expression with the G flag and the great thing is you don't have

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to know what it is.

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We will talk more about regular expressions.

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So let's go ahead and copy this over.

182
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So the first thing you want to do is adapt this code to fit our particular situation.

183
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So we don't need this first variable declaration because we actually have our string coming in as as

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TR.

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But I will need to do is do the replace on as TR in the first place and then we'll want to change what

186
00:12:52,540 --> 00:12:55,590
we're replacing and what we are replacing it with.

187
00:12:55,600 --> 00:13:01,330
So we want to replace dashes and all that I'll say about this syntax here is that this is called a regular

188
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expression.

189
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And whatever we put inside of the slashes is the pattern that it will look to replace.

190
00:13:07,810 --> 00:13:13,280
So if I put something like double dashes it would look for two dashes in a row.

191
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So that's it.

192
00:13:14,500 --> 00:13:20,530
Regular expressions are much more complicated where I can define very long and advanced patterns.

193
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And then I can replace them with something over here.

194
00:13:23,230 --> 00:13:29,390
So then we need to update what we're replacing the dash with which is just an underscore.

195
00:13:30,070 --> 00:13:38,500
So I'm going to save this to a variable called new string a new as TR is the result of running the string

196
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not replace.

197
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The reason I did that is that dot replaced doesn't actually replace anything in the TR in the initial

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string itself.

199
00:13:47,920 --> 00:13:51,520
It just returns a new copy with the replaced data.

200
00:13:51,520 --> 00:13:57,850
So I want to capture that new copy that's returned in the new string variable and then just return new

201
00:13:58,150 --> 00:13:59,520
as TR.

202
00:14:00,190 --> 00:14:02,230
So let's try this out in the browser.

203
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I'm going to refresh my problems that page and try Khabab to snake of Hello Desch worlds and we get

204
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hello underscore world.

205
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Let's try it again with hello world again.

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And you can see it replaces all dashes.

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So that's it there.

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So again the focus in this exercise was really on googling and trying to find information