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alright so the changes we made at the

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end of the last video enable us to send

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the output to a file if you want to

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using the technique we saw back in

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Section 10 when we were writing to

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files

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alright so let's make sure that it still

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works and that it looks the same as it did

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before so now we can send the output to

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a file and see how it displays in a

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browser so lets actually do that so what

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we're going to do is after the

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tag the paragraph tag we're going to do

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....

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....

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...

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....

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...

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....

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and we'll just open the project pane so

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we can see that the file gets

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created for us now if you are using

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linux or mac do make sure you add the

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dot HTML file extension even if you

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wouldn't normally do that and I'll

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explain why in a minute

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now we can send the output of the

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display method to a file by adding test

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_doc as the named perimeter in the

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call to display and you saw me do that on line

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69 so let's just run this you can

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see that was very quick and then the

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file test.HTML appeared now intelliJ

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understands about HTML so i can

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right-click the test file in the project

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pane the context menu their is an open in

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browser down here and that's why I

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mentioned that you should include the

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file extension linux and osx don't

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rely on the file extension to decide

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what to do with the file but

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intelliJ has adopted the windows

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approach and does use the file extension

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so if the file doesn't have a dot HTM or

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dot HTML extension then you won't get

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the option to open in your browser

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alright so in my case though i'm going

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to choose chrome which is the one that I

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normally do when i'm recording videos

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you can choose the default

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browser and we can see that it's

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actually popped up now and it's working

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quite nicely

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alright so that's composition now we've

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used both

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composition and inheritance in this program

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so it's a good example of the

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differences between them and when you

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use each one so getting back to our code

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now our basic classes all inherit from

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tagged and when we talk about head for

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example would say that head is a tag

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similarly body is a tag and so is

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doctype although doc type are slightly

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different kind of tag it doesn't have a

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corresponding end tag so whenever you

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have a relationship that can be

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described using is a that's an

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indication that you should consider

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using inheritance to model the objects

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composition is used when the

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relationship is described as a has a a

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document has a doctype and has a body so

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composition is more appropriate to model

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the document

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ok there's another example of

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composition being used in our body class

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so let's have a look at that HTML

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doc object has to contain a

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doctype a head tag and a body tag so it's

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effectively not an HTML document without

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them

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so these three components are created

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when each instance of the class is

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created in the init method you can see

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its doing that down here starting on line

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47 now body object has any number of

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tags and maybe empty that would make for

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a very interesting document but it would

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actually conform to the specification so

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we don't create any objects when body

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instances are created instead we just

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create an empty list ready to contain

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the tags when they're added you can see

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that code for that here on line 32 now

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when a tag is added to the body by

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calling the body classes add_

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tag method a new tag objects created then

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appended to the list now this is also

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composition but now the body class has

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its own attributes isn't just composed

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of its composite classes

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it has an underscore body _

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contents data attribute and a method

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called add underscore tag

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alright so at this point anything else

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to say about this wil all be repetition

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so it's time for a challenge to

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consolidate what we covered to give you

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a bit of a chance to apply it at the

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moment ahead class doesn't create a

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document header with anything in it

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so your challenge is to modify the

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program so that the head class can

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include a title tag and your HTML should

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look something like this

117
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although there's no need to include

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line-breaks indenting I've just done

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that to make it easy to read but the

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text for the title will be passed to the

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html dot classes init method where

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the documents created alright so that's

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the challenge see how you go with that

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pause the video and I'll see you when

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you get back ok so the basic approach

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this challenge will probably be the same

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for all solutions but you may well have

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a different implementation to my

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solution as always that's fine

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the real test is does it work if you get

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the correct HTML produced then

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congratulations

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alright so if you read through the basic

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HTML structure that we looked in the

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browser earlier you may have noticed

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that the head can contain a few

137
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different tags so you may have made the

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head class behave like a body class with

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an add_tag method to add new content

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to the head element that's fine it's

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probably the way you do things so that

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the program correctly reflects the HTML

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specification the challenge we asked for

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a title so for my solution i'm just

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going to add a title and nothing more

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so the first step is to modify the head

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class and we need to modify the init

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method to take another argument which

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effectively will be the title going to

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come up here we're going to put....

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....

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...

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00:06:09,160 --> 00:06:13,270
...

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....

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...

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...

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....

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...

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....so this creates a new

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tag with the name title and the contents

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being the text that was passed in to the

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init method now the head contents are

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then set to this the string

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representation of this new tag now we

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can improve that slightly

166
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if the title doesn't contain any text

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then we really don't want an empty tag

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inside the head so we can give the title

169
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parameter a default value than test

170
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this before creating the tag

171
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let's go ahead and do that i'm going to

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put....

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...

174
00:07:03,730 --> 00:07:14,360
...

175
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alright next thing we need to do is

176
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modify the HTML dot class now first it

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needs a parameter to the init method to

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accept the title and we'll use a named

179
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parameter with the default value here as

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well that way a document can be created

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without providing a title so come

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down to the html doc the init Method...

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...

184
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...

185
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...now the html .

186
00:07:48,790 --> 00:07:50,420
class doesn't have to do anything with

187
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the title it's just passing it on to the

188
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head class when it creates a new head

189
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object and that should be all we need to

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00:07:56,720 --> 00:07:59,270
do I'm going to start by making sure we haven't

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broken anything so i'm going to run the

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00:08:00,890 --> 00:08:05,140
program if we don't got any errors that is a

193
00:08:05,140 --> 00:08:07,580
good sign and what i can do is open the

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00:08:07,580 --> 00:08:09,580
project pane I can also double-click

195
00:08:09,580 --> 00:08:11,980
that if i wanted to open the HTML file

196
00:08:11,980 --> 00:08:13,670
in the default browser but I'm going to

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00:08:13,670 --> 00:08:15,980
right click it open a browser and choose

198
00:08:15,980 --> 00:08:19,910
chrome again that's it opening up now

199
00:08:19,910 --> 00:08:22,580
in a new tab if we have a look at the

200
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HTML so far so good we haven't past a title

201
00:08:26,390 --> 00:08:28,190
in so we haven't got a title and the

202
00:08:28,190 --> 00:08:29,950
head tags up there on line three

203
00:08:29,950 --> 00:08:32,830
so that's good that's working so let's

204
00:08:32,830 --> 00:08:34,730
see now if it works when we do passing a

205
00:08:34,730 --> 00:08:36,549
title and i'll provide that when we

206
00:08:36,549 --> 00:08:39,789
create the HTML doc instance go back

207
00:08:39,789 --> 00:08:40,700
to the code again

208
00:08:40,700 --> 00:08:44,470
so where we need to change this is on line

209
00:08:44,470 --> 00:08:48,140
67 let's just make that....

210
00:08:48,140 --> 00:08:52,210
....all right we'll run

211
00:08:52,210 --> 00:08:57,340
again in a browser or open in browser and

212
00:08:57,340 --> 00:08:58,720
look at the source

213
00:08:58,720 --> 00:09:01,900
okay for some reason we haven't got a

214
00:09:01,900 --> 00:09:03,070
a title lets just go back and check our

215
00:09:03,070 --> 00:09:08,080
code ok looking at the code

216
00:09:08,080 --> 00:09:09,700
definitely got the title in there and we go

217
00:09:09,700 --> 00:09:12,260
back down I'll go back up i should say

218
00:09:12,260 --> 00:09:13,130
to the head

219
00:09:13,130 --> 00:09:15,860
we've definitely got the title

220
00:09:15,860 --> 00:09:18,700
arguments showing init method and we're

221
00:09:18,700 --> 00:09:21,760
definitely creating a tag and that should all

222
00:09:21,760 --> 00:09:23,470
be ok as far as I'm concerns just try

223
00:09:23,470 --> 00:09:28,010
running it again and go back to browser

224
00:09:28,010 --> 00:09:29,570
what we need to do is need to open it

225
00:09:29,570 --> 00:09:35,440
again open browser Chrome again let's

226
00:09:35,440 --> 00:09:38,360
just look at the page source and it is

227
00:09:38,360 --> 00:09:40,210
....

228
00:09:40,210 --> 00:09:43,720
...

229
00:09:43,720 --> 00:09:46,310
...

230
00:09:46,310 --> 00:09:50,650
...ok so false alarm

231
00:09:50,650 --> 00:09:52,690
that was all working correctly and with

232
00:09:52,690 --> 00:09:55,190
now got the test html containing a

233
00:09:55,190 --> 00:09:58,330
title tag inside the head and by the way

234
00:09:58,330 --> 00:09:59,470
the other way we could have checked for

235
00:09:59,470 --> 00:10:01,880
that is if we just go back and

236
00:10:01,880 --> 00:10:05,870
closed down these view sources depending on

237
00:10:05,870 --> 00:10:07,880
the browser you can actually see the

238
00:10:07,880 --> 00:10:10,570
title in the browser bar but I can't the way

239
00:10:10,570 --> 00:10:11,890
chrome is configured on my

240
00:10:11,890 --> 00:10:13,660
computer right now that would be a

241
00:10:13,660 --> 00:10:15,740
second way of doing it anyway because in

242
00:10:15,740 --> 00:10:17,360
my case I'm still just seeing the URL of

243
00:10:17,360 --> 00:10:21,910
the document but depending on how your

244
00:10:21,910 --> 00:10:24,010
browser is configured you probably see

245
00:10:24,010 --> 00:10:25,810
the title in the browser's address bar

246
00:10:25,810 --> 00:10:26,590
anyway
the title in the browser's address bar

247
00:10:26,590 --> 00:10:28,810
alright so that's it that's composition

248
00:10:28,810 --> 00:10:30,970
in action in the next video we're going

249
00:10:30,970 --> 00:10:32,020
to look at something that's often

250
00:10:32,020 --> 00:10:33,740
described as a weaker form of

251
00:10:33,740 --> 00:10:36,700
composition and that's aggregation see

252
00:10:36,700 --> 00:10:42,450
you in the next video