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All right guys so in the last video we looked at all the different functions that we can use to evaluate

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regular expressions but we didn't really look at some of the you know patterns in some of the Medak

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characters and symbols we can use things like that.

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So that's what we're going to do in this video but before we want to do that I want to create a custom

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function that will basically console log and say whatever we put in contains the regular expression

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or I'm sorry the regular expression contains whatever we put in or does not contain whatever we put

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in.

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I'm just a cleaner way of handling the result.

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OK so let's go ahead and create a function and we'll just call this our e test for regular expression

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test.

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All right.

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And we're actually going to use the test method.

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We're going to say if and actually this is going to take in two things the regular expression and the

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string and we're going to say if our e door test wrapped the string then we want to console dot log

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and we're going to put in some tactics here and we're going to say that the string

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matches the rebought source OK because the rebought source will keep out the the slashes and just give

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us the expression else then what we want to do we want to console log.

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I was just grab this OK and this time we're going to say does not match the regular expression.

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This should actually be matches.

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All right.

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And then I also want to do exact as well.

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Right above it.

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So it's just I'm just to just to give us another type of output.

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So we'll say Konst Konst as TR.

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This is what will actually be editing the string we'll be editing and then we'll also do Consta result

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equals Ari dog exec and then pass in the string and then log the result.

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See a console log result.

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All right.

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So we'll get to logs let's put a comment here also a string to match and then this will be

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Lague results.

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All right.

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And we just finally want to call this function retest and pass an r e to and destroying.

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All right.

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So now we're going to go up above here and this is where we're going to start to create our regular

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expressions so let's say let R E and then I'm just going to keep going down and and redefining r e so

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we can do our tests.

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All right.

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So we already talked about literal characters.

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All right.

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So if we were to say R E equals and then put our slashes in to represent an expression literal and say

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hello and then and here we'll say hello world and save and you can say you can see no we're getting

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no from this part from the exam.

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And then we're getting hello world which is the string does not match hello which is the expression.

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And the reason it doesn't match is because we don't have the case the case sensitive flag.

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So if we were to add the I hear and save now it will match ok because it's case insensitive so you can

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see we're going to get the result array from the exec and then we're also going to get our little custom

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message from our custom retests function.

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All right so that's how this is going to work.

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Now let's step away from just the literal characters.

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Well we're going to use literal characters along with Medich characters symbols.

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All right so let's say Metta character symbols and there's different types of Medak characters.

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These are just these are symbols that we can use.

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So let's say our equals and let's look at the carrot symbols so this is the six shift six character

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and then we're just going to put an H here.

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And let's also use the I flag.

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All right so what this means what this does is it means must start with.

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OK so if we go Henry run this we're going to get basically a true k.

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Hello matches this expression because it's saying that whatever this is the string and has to start

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with an H and it can be case insensitive.

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If I were to remove that I then we're going to get now.

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And it does not match.

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All right but I'm going to keep the case insensitive flag.

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Now if I were to put Brad hello world and say we're going to get.

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No we're not we're not going to get a match because it's not starting with the letter H.

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Ok if I were to put an H here H rat or whatever that will work because it's starting with the letter

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H.

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Ok so just remember this symbol means start with OK and at the same time we have ends with.

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So Samos ends with.

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And that's the money sign.

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All right.

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Now this string hello world ends with a D.

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So let's go ahead and put a money sign after it.

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So this is saying it must end with a D save and run and we get ok it matches you can see the indexes

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at 10 which is right here.

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Now it doesn't have to be just one character.

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We could do the word world.

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And that would match because it is in fact ending with the word world.

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We could even do a lower case because we have the the case insensitive flag.

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OK but if we did like f world and say that's not going to work if we did space world that will work

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because we're basically going from here over and space world matches.

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All right.

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So hopefully that makes sense.

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So.

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So carrot is start money signed.

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And just remember that right now you can also do begins with and ends with.

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So if we were to say

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let's say hello like that and then let's put the money sign at the end and the carrot sign at the beginning.

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That means that even if we have hello world here if we save we're going to get a not a match.

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Hey we're going to get.

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No because what this is saying is that it can only be how low it has to start with hello and with hello

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So if I were to get rid of this and save that we'll match.

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All right so put a comment here and will say must begin and end with.

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All right so the next thing we'll look at is the dawn of the period character and this means that it

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can match any one character.

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So what I'm going to do is just copy this and let's replace the e with a dot.

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All right so this will say matches any one character.

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So if we go ahead and save this and run this will pass.

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Now this will also pass if I put in let's say R and save.

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That'll pass.

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If I put in the old one.

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That'll pass if I put in a symbol that will pass anything here.

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I can put in place of this dot.

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It's basically like a wild card.

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Now the difference between this and the asterisk which will look at next which is the actual wildcard

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is it has to be one character for instance I couldn't say you know e e like that.

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If I do that it's not going to match because this is two extra characters.

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This defines one.

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All right.

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Now let's try it with the asterisk

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if I were to do that what this does is it matches any character zero

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or more times.

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OK.

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So if I go ahead and run that see what work I want to remove or move the start and finish from both

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of these.

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OK.

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So we save that and that works.

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And the reason it's working is because the actress represents any character zero or more times so zero

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we don't even need that value there so I could remove it completely.

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And that still matches.

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All right.

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So that's a complete wildcard including nothing at all.

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All right so now let's take a look at the question mark which is an optional character.

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So what am I going to do is give you an example here of something you may you might actually use and

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that is the word gray.

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OK so when we have the word gray sometimes it's spelled with an A Sometimes it's spelt with an e.

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So what I want to do is have an optional carrot an optional a or an optional E..

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And the way that you define that is by putting a question mark after the character that's optional.

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So we're going to say it is optional and is optional and then a is optional.

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Right.

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So let's go over here and just say optional character and then down here let's put in gray.

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See if that matches it does ok we get our response back.

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And if I put an e here and save that matches if I put in I in save we get.

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No.

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All right.

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Now since both of them are optional I can also just do G.R..

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Why.

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And that will still work OK because they're both optional.

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All right.

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I'm going to show you another way of doing this as well.

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But for now the next thing I want to show you is escapin characters.

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All right.

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So actually let me just bring that down I'll say escape characters.

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Now what if we wanted this to be gray with an actual question mark in the question mark being used as

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a literal.

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So to escape something just like you would with you know a regular javascript's string you want to use

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you or your backslash.

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OK so let's put a question mark here.

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Now if we leave it this way it's basically saying that y is optional.

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So if I save this this will work but it's basically saying Y is optional so I can put like a 4 here

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if I want.

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And that will still work.

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And that's not what I want it for I want it to be.

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I want the questionmark to be a literal.

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So I'm going to prefix it with a backslash.

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So now I'll save and it works it's a match and if I try to change the Y to like are we get.

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No.

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Because it's no longer optional.

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The question mark is just being taken as a literal.

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All right so these are some of the meta characters symbols now in the next video.

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I'm going to continue with this same file and we're going to take a look at using brackets which are

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used for character sets as well as braces curly braces which are quantifiers and then parentheses which

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are used for grouping.

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All right.

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So I will see you in the next lecture.