0:00:00.000,0:00:03.184
Now let's go ahead[br]and make another constructor.

0:00:03.184,0:00:07.043
So this time,[br]I'm going to create a Dalmatian class....

0:00:09.180,0:00:12.553
And it's going to be a dog[br]with the color...

0:00:15.770,0:00:19.907
[slowly][br]white with black spots.

0:00:22.995,0:00:25.050
But obviously, I haven't...

0:00:25.050,0:00:27.660
created any kind of relationship[br]between "Dalmation"

0:00:27.660,0:00:30.540
and "dog" just yet, so if I reload--

0:00:31.631,0:00:33.741
oh! Syntax error.

0:00:36.347,0:00:39.176
Let's see where that is....

0:00:39.176,0:00:42.060
Oh, I forgot my parentheses.

0:00:42.060,0:00:43.712
This is a function.

0:00:48.767,0:00:52.880
So obviously, if I set "spot"

0:00:53.940,0:00:55.712
to new...

0:00:57.529,0:01:01.333
Dalmation, Dal-ma-tion....

0:01:04.319,0:01:06.665
Let's try that again.

0:01:06.665,0:01:09.000
So now "Spot" is a dog,

0:01:09.000,0:01:11.194
but only the color property[br]is set.

0:01:11.194,0:01:14.857
So I can say "spot.color,"[br]and that works fine,

0:01:14.857,0:01:17.753
but if I say "spot.speak,"

0:01:18.729,0:01:20.130
that doesn't work at all.

0:01:20.130,0:01:24.030
So, in order to define[br]the inheritance relationship,

0:01:24.030,0:01:26.040
I need to do something[br]a little odd.

0:01:26.040,0:01:28.260
So let me give you[br]a little background first.

0:01:28.260,0:01:30.630
So, if you're used to a language

0:01:30.630,0:01:35.190
like C++ or Java or C#,

0:01:35.190,0:01:38.254
then the way that you define[br]an inheritance relationship

0:01:38.254,0:01:41.730
is you have a base class,[br]like dog,

0:01:41.730,0:01:44.040
and then you extend[br]that base class

0:01:44.040,0:01:47.387
by creating a subclass, like Dalmation.

0:01:47.387,0:01:49.470
So...

0:01:49.470,0:01:51.750
the way you do it in JavaScript

0:01:51.750,0:01:53.010
is a little different.

0:01:53.010,0:01:56.220
So JavaScript is known[br]as a prototypal

0:01:56.220,0:01:58.530
or "proto-tip-pal" language,

0:01:58.530,0:02:01.500
where inheritance is based[br]on prototypes.

0:02:01.500,0:02:02.908
So what is a prototype?

0:02:02.908,0:02:05.372
A prototype is an object.

0:02:05.372,0:02:08.220
So the way you define[br]an inheritance relationship

0:02:08.220,0:02:12.330
is you set a base prototype,[br]a base object,

0:02:12.330,0:02:15.797
that the sub-object[br]that you're creating

0:02:15.797,0:02:18.210
inherits all the properties from.

0:02:18.210,0:02:20.703
So instead of extending a class,

0:02:20.703,0:02:23.397
which is a blueprint[br]for a set of objects,

0:02:23.397,0:02:26.640
instead,[br]you're extending an object

0:02:26.640,0:02:29.730
by adding additional methods[br]and additional properties

0:02:29.730,0:02:32.400
to the base set of objects[br]and properties

0:02:32.400,0:02:34.530
that that object has.

0:02:34.530,0:02:36.210
So what I want to do, basically,

0:02:36.210,0:02:39.000
is I want to create a new dog,

0:02:39.000,0:02:42.330
which is the prototype for all Dalmations,

0:02:42.330,0:02:44.610
and then I want to inherit

0:02:44.610,0:02:47.010
that prototype

0:02:47.010,0:02:49.950
for all Dalmations that I create.

0:02:49.950,0:02:52.170
The way that works is the constructor,

0:02:52.170,0:02:53.850
the Dalmation function,

0:02:54.390,0:02:57.540
has a prototype property, which is an object.

0:02:57.990,0:02:59.700
So whenever you create a function,

0:02:59.700,0:03:01.470
there's going to be a prototype property

0:03:01.470,0:03:03.570
for that function, let's take a look at it.

0:03:03.960,0:03:05.190
So Dalmation,

0:03:06.540,0:03:07.920
which is a function.prototype,

0:03:11.820,0:03:12.960
is an object

0:03:14.040,0:03:16.350
with a constructor function, and actually,

0:03:16.350,0:03:18.780
this constructor function, if I open this up,

0:03:19.650,0:03:21.420
the function is Dalmation.

0:03:21.450,0:03:25.110
So an object whose function, constructor function,

0:03:25.110,0:03:28.440
is a Dalmation, is the prototype

0:03:28.530,0:03:30.660
for all Dalmation objects.

0:03:31.350,0:03:33.450
And there aren't any other properties

0:03:33.450,0:03:36.180
that are really interesting or useful on this object,

0:03:36.180,0:03:39.090
because I haven't set any, but for example,

0:03:39.360,0:03:50.610
if I set Dalmation.prototype.legs = 4...

0:03:52.140,0:03:54.810
And then I said, spot.legs,

0:03:56.010,0:03:58.800
all of a sudden, Spot, an existing Dalmation,

0:03:58.800,0:04:01.350
inherits the number of legs

0:04:01.650,0:04:05.130
from the prototype of the Dalmatian class.

0:04:06.330,0:04:11.460
So I can do this for other properties as well.

0:04:11.490,0:04:14.940
So dog.sound is bark,

0:04:17.550,0:04:20.730
spot.sound is now bark as well.

0:04:21.810,0:04:24.510
And this will be true for any other dog that I create.

0:04:24.540,0:04:33.870
So for example, Rover is new Dalmation as well.

0:04:33.870,0:04:35.760
rover.legs is four,

0:04:36.840,0:04:39.270
rover.sound is bark,

0:04:39.900,0:04:42.960
but I still haven't set a property

0:04:44.100,0:04:47.130
for speak, so that's still going to be an error.

0:04:48.780,0:04:52.170
So this suggests a way of doing inheritance,

0:04:52.170,0:04:55.260
which is to make sure that all of the properties

0:04:55.260,0:04:57.690
defined for dog are also set

0:04:58.200,0:05:01.650
for the prototype object for the Dalmatian class,

0:05:03.060,0:05:05.220
and there's a really easy way of doing that,

0:05:05.460,0:05:06.510
which is...

0:05:07.710,0:05:15.480
Dalmation.prototype = new Dog.

0:05:18.000,0:05:20.760
So Dalmation is going to have a prototype object

0:05:20.760,0:05:22.020
because it's a function,

0:05:23.130,0:05:27.120
but I'm overriding that default generic object

0:05:27.180,0:05:29.850
with a new dog.

0:05:30.810,0:05:32.940
So any new dog that I create

0:05:33.000,0:05:35.070
is going to have all of the properties

0:05:35.070,0:05:36.390
that are defined for dog.

0:05:37.080,0:05:39.660
So let's go ahead and-- actually let me save this...

0:05:40.320,0:05:41.220
Save...

0:05:42.120,0:05:43.470
and then reload,

0:05:44.640,0:05:49.710
and now, I'm going to create Spot is new Dalmation.