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So that was a very basic class.

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Now when building classes they often get more complex than that.

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And you might want to store more data under let's say a department also should have employees that could

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be an array and initially it might be an empty array.

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And to also be a bit more precise about what you want to store in there.

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It could be a string array to keep it relatively simple.

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Now we could have a method here at employee there.

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We want an employee as our argument which should just be a string in our example and then we can set

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this employees push so push a new employee onto our employees array with this code.

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Now we could all add another method print employee in for Mason

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and there I went to console log this DOT employees dot length and I also want to console log this DOT

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employees itself.

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Now if we go down here now we can come it out this code here would which would break again because we

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again don't fit the department description with our object down there and instead here on this accounting

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department we can add an employee let's say Max and another employee let's say menu and then besides

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describing it I also want to get my employee information on there.

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If we safeties we should get this output to employees and here's some information.

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Now that's all nice to have one problem we have with this class is that we could change employees from

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outside not only with an employee but by directly accessing the employees property just as we can do

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it for the name as well by the way.

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So what I mean is we could also go to accounting and then reach out to employees and maybe add another

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employee at index 2 and they're Pozen and I like that if we do that and we save it we get free employees

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and we get Anna.

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Now you might think well great we got no way.

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Well when building more complex applications you typically want a wide something like this don't you

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want to make sure that there is one clear path.

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One way of using your class and that things like that.

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Alternative ways of using it are not really supported because if you're working in a bigger team well

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then one colleague is going to use this approach for adding an employee and no colleague might use this

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approach and you don't want this you want to have one uniform way of doing this also because maybe in

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the ad employee method you do more than just add it to the array maybe you first of all want to have

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some validation etc. in here.

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So you might have extra code in there which simply does not execute if you directly assign a new value

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or add a new value to the array with this line here.

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So you don't want to permit that employees is accessible like this from outside of the class.

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And typescript Scott you covered you can turn employees here into a private property a private field

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by adding the private keyword in front of it.

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Now what private means is that employees is now a property which is only accessible from inside the

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class.

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So from inside the created object.

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So any method inside of the department class is able to still work with employees but you can't access

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it like this anymore.

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Here you see him now getting an error that tried to save.

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Does I get a compilation error that the property employees as private and only accessible within the

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class department.

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So now we forest dead when employees should be added to this department.

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People have to use the add employee method because they get an error or if they write code like this.

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This is a so-called modifier here.

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The private keyword and besides private we all got public which is the default though you don't need

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to add public so name like this is exactly the same as name with public in front of it.

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The difference is that public properties are accessible from outside.

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So for example here I could also reach out to name and assign a new name here if I wanted to.

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That is possible for private properties.

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This year is not possible we can only use them from inside.

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Technically by the way javascript doesn't know public and private only in very modern versions added

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recently such a thing exists in the past.

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Javascript didn't know private or public properties all properties always were public there typescript

58
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introduces this feature which of course does not work during runtime however because javascript.

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Until recently only new public properties.

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So this line here frozen area during typescript compilation.

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If you compile it to JavaScript nonetheless this code would still executed runtime without errors because

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again javascript on its own until recently didn't notice concept.

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So depending on the where's your compiling for it still won't know it and therefore typescript only

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supports this because it checks it during compilation not at runtime with it.

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However we can a wide code like this and force everyone to write cleaner code.