Add Add Generic Typing To An Anonymous Function as a TypeScript TIL

typescript/add-generic-typing-to-an-anonymous-function.md

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+# Add Generic Typing To An Anonymous Function
+
+A common pattern, especially when dealing with collections of data (read:
+arrays), is to have a function that can transform an array of any type of data.
+In order to keep this kind of function general-purpose and have it preserve
+types, we'll need to use generics.
+
+For an anonymous function to work with a generic type, it needs to open with a
+signature for the generic type:
+
+```typescript
+<T>() => {}
+```
+
+With that in mind, we can write a function that accepts an array of type `T`,
+does something to that collection, and then returns an array of type `T`.
+
+For instance, here is a function that takes the first `n` elements from the
+array and returns them.
+
+```typescript
+const take = <T>(arr: Array<T>, n: number): Array<T> => {
+  return arr.slice(0, n)
+}
+```
+
+This both enforces and preserves the type of the array. It works well for
+situations where the array is a bunch of complex objects with specific types
+like we'd get from a Prisma query.