Using Generic in TypeScript about types in the Code

By Md Shoriful Islam

# Using Generic in TypeScript about types \<T> in the Code



## Question 1: Here what is this <T> means?

```typescript

const addID = <T>(obj: T) => {

  let ID = Math.floor(Math.random() * 100);

  return ({...obj, ID});

}

```


## Answer 1:

In the code snippet you've provided, `<T>` is a **generic type parameter** in TypeScript. It allows you to write a function that can work with any type of object while still maintaining that object's specific type information. When you use the function `addID`, you can pass in an object of any type, and TypeScript will understand that the returned object will be of the same type as the input, plus the additional `ID` property.


Here's a breakdown of how it works:


```typescript

const addID = <T>(obj: T) => {

  let ID = Math.floor(Math.random() * 100);

  return ({...obj, ID});

}

```


- `<T>`: Declares a generic type `T`.

- `(obj: T)`: Indicates that the function takes an argument `obj` of type `T`.

- `return ({...obj, ID});`: Returns a new object with all properties of `obj` plus a new property `ID`.


When you call `addID`, you can pass in an object of any type, and the function will return an object of that type with an `ID` added to it. For example:


```typescript

let user = { name: "Alice" };

let userWithID = addID(user);

// userWithID is now { name: "Alice", ID: some_random_number }

```


In this example, `userWithID` maintains the `name` property from `user` and adds a new `ID` property with a random number. The type of `userWithID` is inferred to be the same as `user`, but with the additional `ID` property.


## Question 2: What is the Full name of this T of \<T>


## Answer 2:

The `T` in `<T>` doesn't have a "full name" — it's simply a placeholder representing a type variable in TypeScript's generic programming. Think of `T` as a label for any type that you will pass to the function when you call it. It's not an acronym or abbreviation for a longer term; it's just a convention to use `T` (short for "Type") as a generic type parameter.


When you define a function with a generic type parameter like `<T>`, you're telling TypeScript that this function can accept any type, and `T` will be replaced with the actual type you use when you call the function. Here's a simple example:


```typescript

function identity<T>(arg: T): T {

  return arg;

}


let output = identity<string>("myString");

```


In this case, `T` is replaced with `string` when calling the `identity` function, and the function returns a string. You could also call `identity` with other types, like `number` or `boolean`, and TypeScript would replace `T` with that type in the function's definition for that call.

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