Consider this `getName` function:

```typescript
export const getName = (params: { first: string; last: string }) => {
  if (params.last) {
    return `${params.first} ${params.last}`;
  }
  return params.first;
};
```

Reading the code, we can see that we don't need to pass in a `last` name in order for the function to work.

However, TypeScript doesn't know that yet.

We have an error with our "Should work with just the first name" test:

```text
Argument of type '{ first: string; }' is not assignable to parameter of type '{ first: string; last: string; }'.
Property 'last' is missing in type '{ first: string; }' but required in type '{ first: string; last: string; }'.
```

## Challenge

Your challenge is to figure out how to type the object so that `last` is optional.

TypeScript can’t tell by itself if your code will still work when object properties are missing. For these situations, you need to specify which are optional.

This is a one character solution.

Adding a `?` before the colon tells TypeScript that the property isn't required in order for the function to work.

With this update, we don't have to pass in a `last` if we don't want to:

```typescript
export const getName = (params: { first: string; last?: string }) => {
```

Adding `?` will also work when using named types, or anywhere else object keys can be specified.

```typescript
type Params = {
  first: string;
  last?: string;
}
```

Tooling in VS Code is smart enough to recognize if a key is optional. This can be seen in the autocomplete, where you will be reminded that `last` should be either a string or undefined.

If you have prior experience with TypeScript, you might have seen a type explicitly set to `string` or `undefined` as seen below:

```typescript
type Params = { first: string; last: string | undefined }
```

However, written this way we do have to pass `last`. More on "or" later.

If you want to set a property as optional, use the `?`.

Denote an Optional Property

0:00 The trick here is to add this little character just before the colon. When I remove it, we go back to basically the problem set-up. What this does is it means that you do not need to pass this in order for this to work.

0:15 I can extract this to a type if I want to. Type params equals this, and it will work in there too. Anywhere that you can specify an object key, you can use this. It means that I can pass this last if I want to.

0:30 You notice that, without this, if I remove it again and I go on the autocomplete, there's no question mark after that last just there. Whereas, if I add that, then I get the question mark saying I could pass either a string or undefined. That little or will come up later, but it's a nice way of saying it.

0:52 An alternative, if you've got a little bit of experience with TypeScript, is you could do last or undefined here, but this means you do need to pass in something in there. I could say last is undefined, and that would make it happy, but adding that little question mark character means that I don't even need to pass the property.

Set Properties as Optional

0:00 Your next challenge is a function called getName here, where you parse in a params object with the first name and the last name here, except you don't need to parse in the last name.

0:14 TypeScript doesn't seem to know this yet. It's moaning at me here by saying, "Property 'last' is missing in type blah blah blah but required in this one."

0:24 It's telling me I do need to parse the last name here. I don't want to. Figure out a way that you can type this object where last is optional.

Get hands-on interactive practice with this free TypeScript tutorial and learn the foundational knowledge and skills you need to become a TypeScript Wizard.

In this TypeScript tutorial you will:

* Learn to type variables, functions, and errors
* Become familiar with the TypeScript documentation
* Gain experience with modern TypeScript tooling

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## Instructions

This Beginner’s TypeScript tutorial is split into several exercises. Each features a `problem` that encourages you to take an active, exploratory learning approach to finding a `solution`.

To attempt a solution, you’ll need to:

1. Watch and read the `problem` introduction.
2. Check out [the TypeScript docs](https://www.typescriptlang.org/docs/).
3. Search for relevant keywords.
4. Give it a go to see if it solves the problem (there may be more than one solution!)

Whether you succeed or get stuck, watch & read the `solution` and check out the included code.

### Prerequisites

You’ll need a working understanding of JavaScript.

### Running the Exercises Locally

Clone [the Beginner’s TypeScript Tutorial repo](https://github.com/total-typescript/beginners-typescript-tutorial), and use npm or yarn to install dependencies.

If you [follow this link to use gitpod](https://gitpod.io/#https://github.com/total-typescript/beginners-typescript-tutorial), you can work in a full VS Code coding environment running in your browser.

Follow the [instructions in the README](https://github.com/total-typescript/beginners-typescript-tutorial) for more.

Free interactive video tutorial that will help you get started with TypeScript.

Beginner's TypeScript Tutorial Repo

First thing’s first: dealing with the implicit ‘any’ type error.

Fix the Implicit 'Any' Error

The Implicit ‘Any’ Type Error

Not all of the functions you write will take primitive types. When you need to pass objects as parameters, there are a few different ways to type them properly.

Add Types to Object Params

Working with Object Params

Just as we saw with object properties, function parameters can be set as optional as well.

Mark a Function Parameter as Optional

Optional Parameters

Assigning types to variables allows TypeScript to provide more useful error messages on the lines where they occur.

Make a Variable Conform to an Interface

Assigning Types to Variables

TypeScript allows us to constrain a property’s value to one of a set number of things. For example, a medal that could only be gold, silver, or bronze.

Delineate Types a Value Can Be

Constraining Value Types

Arrays are one of the most common data structures in development. In this lesson, find out how they are represented in TypeScript.

Two Ways to Represent Arrays

Working with Arrays

Being strict about what is returned from your functions ensures that your code is safe on the inside as well as the outside.

Annotate a Function to Specify its Return Type

Function Return Type Annotations

Almost every web application involves making API calls. But how can we tell TypeScript what to expect when we’re expecting data?

Update Return Type Annotations for Async Functions

Typing Promises and Async Requests

One of the most crucial TypeScript concepts to understand is how type arguments work with certain functions and constructors.

Pass a Type Argument to Restrict Potential Types

Passing Type Arguments

Seeing “index” in a type error message usually refers to the key of an object. In this lesson are a few techniques for properly typing dynamic object keys.

Techniques for Typing Dynamic Object Keys

Assigning Dynamic Keys to an Object

TypeScript offers powerful features for narrowing down branches when working with third party APIs or functions that support data in different forms.

Change Function Returns Based on Type

Narrowing Down Union Types

When using a try-catch in TypeScript, it’s important that you type the error appropriately. There are a few different techniques to accomplish this.

Techniques for Coercing an Unknown Type

Typing Errors in a Try-Catch

Interfaces can inherit properties from other interfaces. This allows us to DRY out our code and have a neater way to work with complex data models.

Extend Interfaces From Other Interfaces

Inheriting Interface Properties

TypeScript allows for composing types together to create new types. This is useful when returning data that is a combination of multiple different types.

Combine Inline or at the Type Level

Combining Types to Create New Types

TypeScript provides us with tools for being more selective when creating new types based on others.

Two Techniques for Creating New Types Based on Others

Selectively Construct Types from Other Types

TypeScript supports typing functions that are passed in as arguments, including the arguments that they take.

Specify the Type of a Function

Typing Functions

TypeScript supports typing the returns from asynchronous functions– great for real world processes like fetching from databases or other third-party APIs.

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Set Properties as Optional

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