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Now besides objects we also have arrays in JavaScript very important type of data arrays are created

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like this in javascript.

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As you know and you can store any data in their numbers strings boolean as objects of a race you can

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have nested Arrays after all and you can also mix data.

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You can have an array with strings and numbers mixed and types with all the supports arrays any javascript

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array is supported and the types of the array can be flexible or strict.

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Now let's have a look at that in typescript for that here in Apt.

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Yes.

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Let's say our person also has a hobbyist key.

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But of course we could also have a variable or a constant hobbies outside of the object.

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So using arrays is exactly the same inside of objects and outside of them.

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So here we have hobbies and hobbies could be sports and cooking let's say.

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So I have two elements in there and these elements as you can tell are strings.

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Now if you hover over a is typescript correctly detected that this of type String array.

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Now that's a syntax you haven't seen before but this is how typescript describes an array of data.

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You have to square brackets and in front of that the type of data which is stored in there.

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Now this is the type type inferred it sorted here we have an array and that we only have strings in

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there.

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So it inferred that Hobbes probably should be the array of strings and indeed for Hobbes that makes

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a lot of sense.

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Of course you can also explicitly set the type of a variable if we would add a new variable favorite

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activities.

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And initially that should be empty then we might want to explicitly set the type of data stored in there.

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Now let's say that should be an array of strings.

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Well then we can just repeat what we just saw type string and then square brackets thereafter and this

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tells typescript what we store in here is not just a single string.

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It's an array of strings.

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And indeed if I try to store just sports and there I get an error I get an error because that here is

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a single string and not an array of strings.

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I don't get an error of course if I wrapped as into square brackets and therefore effectively I create

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an array.

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I again do you get an error though if I add a number let's say because we defined this to be an array

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of strings.

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Now here we have a mixed array.

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It's an array of strings and numbers.

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So that does not work and is not supported here.

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If we would want to support such a mixed array one solution would be to use any here.

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D any type is a special type and typescript which will have a closer look later which basically means

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do whatever you want.

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It's of course a type you don't want to use too often because you'll lose the benefits typescript gives

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you your back and JavaScript the world where you also can use any value anywhere.

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So any is really flexible but the flexibility comes at the price of basically giving up all benefits

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types good offers.

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So hero when I go back to string because a re don't want to have a number in there and hence we can

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remove the number and we're good erase all that give us a great example.

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Actually just like objects and their properties.

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How dynamic type scripts type inference is if we add a for loop here at the bottom and we want to go

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through all the hobbies of person.

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We can of course use a traditional for loop with for const hobby of person dog hobbies.

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So accessing the hobbies property and going through all the hobby stair storing each hobby for each

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iteration in this constant.

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And then we can console log hobby here.

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Now that's not too fancy.

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That's something we know from javascript right.

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If I now compiled is apt yes file down their we get the name from this line and they're after the two

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hobbies being printed but what's actually interesting here is that on hobby we can access anything we

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can access on any string for example to upper case.

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I get this all to completion and typescript does not complain.

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Why does it not complain because it knows that Hobbes is of type String array.

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So when I access persons that Hobbes type scripts inference detects that Hobbes will be an array of

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strings.

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So a hobby on the other end is correctly identified as being a string because since we go through an

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array of strings Well the individual values have to be just strings and therefore typescript offers

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us great support down there and allows us to do anything with hobby that can be done with a string because

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it knows with certainty that hobby will be a string because of the types we setup up there.

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And that's really flexible in of course a great feature which makes writing code a lot easier and way

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more flexible and secure.

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For example we would get an error here if it would try to access hobby dot map.

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If I thought this would be an array the map method is available on arrays but not on strings and here

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correctly I get an error.

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That map does not exist on type string because it doesn't.

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So here we get an error and that's good that we get it because this would be wrong.

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And here we see typescript inference really really shine.