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- Now in this course so far

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we've talked a little bit about

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when TypeScript just assumes a variable

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can be any type at all.

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For example, if I define the variable A,

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and I don't give it a default value

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and I don't give it any type information,

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it just assumes that A can be anything.

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So I could set it to a number here,

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I could set it to a string,

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it's going to work just fine

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'cause TypeScript says, "I
don't know what this is.

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It could be literally anything."

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And TypeScript actually has
a specific type for that

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and that is called the any type.

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As you can see inside of here,

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if I hover over this,

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this is inferred as the type any.

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And I could manually
type this as any as well

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by writing out any like this.

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And that's going to mark
this as an any variable.

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So even if I give it a
value of four, for example,

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it still says that this can be anything.

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So it doesn't matter what I assign it to,

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whether it's an object, an array,

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a number, a string, it doesn't matter,

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TypeScript says this could be anything.

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Now the great thing about this

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is it means you can just write your code

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like normal JavaScript,

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'cause JavaScript, every
variable is any type by default.

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But obviously the downside is you lose

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pretty much all of the benefits

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of TypeScript when you use any.

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For example, I no longer
have any auto complete

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because it doesn't know what this is.

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It doesn't know is it a
string, is it a number,

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is it a Boolean, is it an array

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is it an object, is it a date?

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It has no idea.

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So you can't get any auto complete

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and you really don't get
any error protection as well

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because again, TypeScript
doesn't know what this is.

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so it can't prevent errors,

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'cause it doesn't know what
it's trying to prevent.

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So really any is a bad idea.

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And most often when
you're writing out code

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if you're writing any like this,

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that's generally a code smell

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and something that you
should not do in your code.

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You almost always want to remove anys

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anywhere that they show
up inside of your code.

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Now for the most part,

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you probably won't run into problems

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with any showing up in your code,

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unless you obviously
manually add them yourselves

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or you're creating a variable

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without actually giving it a value

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or you give it a default value

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of like null or undefined,

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which in that case

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it's always going to be a
default value type of any here.

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But the other scenarios where you may run

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into any that you need to be aware of,

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is if you use json.parse,

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you pass at some string.

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The actual return of
json.parse is going to be any,

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for example if I say
const A is equal to that

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and I hover over this,

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you can see it has a type of any.

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And that's just because TypeScript

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doesn't know what the object

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or value being returned
from json.parse is.

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It could literally be anything at all.

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So it just needs to be able to account

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for all of those different things.

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Same thing if you make a fetch request,

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if I make a fetch request to some URL

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and then I want to get my data back,

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so I say res.json,

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now I have my data here that I can use.

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So we'll get data,

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oops, make sure I clean
up my code a little bit.

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There we go.

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And if I go over this data,

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you can see that this
is again a type of any,

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because it doesn't know what the data

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being returned from your API is.

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It could be JSON,

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it could be something entirely different.

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It has no idea.

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It could be unknown, undefined,

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doesn't know, so it just
defaults the type two any.

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So that's something
that's really important

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to make sure you understand

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because you may be using
fetch inside your code base.

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You may have this data
variable that you start

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accessing different properties on.

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And before you know it you realize

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that you're not getting

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the error protection that you need,

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'cause this is inferred as a type of any,

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which pretty much when you use any,

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it just shuts down TypeScript

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for anything that uses that variable

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or piece of code that you've typed as any

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because it just doesn't know what to do.

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Overall, my advice is to never use any,

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unless you're in the
process of maybe converting

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a JavaScript project over
to a TypeScript project,

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which I'll cover much
later in this course.

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But pretty much

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if you're writing TypeScript
code from scratch,

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there's almost no use case

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that you would want to use any in

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because it just essentially
shuts down using TypeScript

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and gets rid of all the
benefits of using TypeScript.