Here's an array of `programModes` wrapped in an `as const`:

```typescript
export const programModes = [
	"group",
	"announcement",
	"1on1",
	"selfDirected",
	"planned1on1",
	"plannedSelfDirected",
] as const;
```

When using `typeof` and `keyof` with indexed access type, we can extract all of the values, but we also get some unexpected values like a `6` and an `IterableIterator` function:

```typescript
type AllPrograms = (typeof programModes)[keyof typeof programModes];

// hovering over AllPrograms shows:
type AllPrograms =
  | "group"
  | "announcement"
  | "1on1"
  | "selfDirected"
  | "planned1on1"
  | "plannedSelfDirected"
  | 6
  | (() => IterableIterator<"group" | "announcement" | "1on1" | "selfDirected" | "planned1on1" | "plannedSelfDirected">)
  | ... 23 more ...
  | ((index: number) => "group" | ... 5 more ... | undefined);
```

The additional stuff being extracted causes the test to fail because it is only expecting the values:

```typescript
type test = Expect<
	Equal<
		AllPrograms,
		| "group"
		| "announcement"
		| "1on1"
		| "selfDirected"
		| "planned1on1"
		| "plannedSelfDirected"
	>
>;
```

## Challenge

Your challenge is to update the `AllPrograms` type declaration so that it only extracts the expected values.

There is a trick to making this work that involves passing a primitive as an argument in the indexed access type:

```typescript
type AllPrograms = (typeof programModes)[unknown];
```

By passing a primitive as an argument in the indexed access type, you can extract values from an as const array.

If you think about it, the keys of the `programModes` array are `0`, `1`, `2`, `3`, `4`, and `5`:

```typescript
export const programModes = [
	"group",
	"announcement",
	"1on1",
	"selfDirected",
	"planned1on1",
	"plannedSelfDirected",
] as const;
```

For example, we can access the first element of the tuple using `programModes[0]`, the second element using `programModes[1]`, and so on:

```typescript
type AllPrograms = (typeof programModes)[0];

// hovering over AllPrograms shows:
type AllPrograms = "group";
```

This tells us that we can create a union of all of the elements by passing in a union of indices into the indexed access type:

```typescript
type AllPrograms = (typeof programModes)[0 | 1 | 2 | 3 | 4 | 5];
```

However, if an item was added to `programModes` we would have to update this union to include the new index.

The better solution is to use `number` as the argument to the indexed access type:

```typescript
type AllPrograms = (typeof programModes)[number];
```

This means that we can add new items to `programModes` without having to update the union, while still being able to index with a specific string like `"group"` or `"announcement"`.

This is likely a design choice made by the TypeScript team to make for a nicer DX.

Using this pattern is a great way to model your data and keep things in sync.

When working with an as const array, passing a primitive as an argument to an indexed access type will extract the expected values.

Pass a Primitive to an Indexed Access Type

Create a Union from an as const Array

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Compiling TypeScript Files to a Directory

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Create a new project with Vite and TypeScript to improve upon our current setup.

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Use Vite for a Frontend App with TypeScript

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When the noEmit option is set to true in the tsconfig.json file, TypeScript acts more like a linter than part of the build process.

TypeScript as a Linter

Comparing Vite with tsc

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TypeScript in a CI/CD System

There is some controversy around whether or not TypeScript should block your dev server when there are errors. Let's explore the pros and cons of different approaches.

Should TypeScript Block Your Dev Server?

The tsx CLI tool allows you to quickly run scripts written in TypeScript.

Quickly Create Scripts with tsx

TypeScript in The Build Process

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Common sense tells us that the booleans in the `add` function should be replaced with some sort of `number` type.

Fixing Errors in the `add` Function

Understanding Function Errors

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Annotating Function Parameters

Annotating Empty Parameters

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TypeScript comes with a set of basic types to help define what kind of values can be assigned to variables.

TypeScript Basic Types

Basic Types in TypeScript

Learn how to make function parameters optional in TypeScript to handle different argument formats.

Using the `?` , add optional parameters in TypeScript functions.

Optional Function Parameters in TypeScript

Optional Function Parameters

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Add a Default Parameter with `=`

Default Parameters in JavaScript Functions

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Annotating with {}

Typing Object Literals

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Making Object Property Types Optional

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Creating `type` Aliases

A Single Source of Truth for Type Definitions

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Learn about the two different syntaxes for defining arrays in TypeScript.

Two Syntaxes for Arrays

Add an Array to an Object

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There are few different ways in which an array of objects can be expressed

Representing an Array of Objects

Arrays of Objects in TypeScript

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Learn how to use rest parameters to pass an indefinite number of arguments of the same type to a function in TypeScript.

Using Rest Parameters in TypeScript

Rest Parameters in TypeScript

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Using Tuple Syntax in TypeScript

Tuples for Precise Array Structures in TypeScript

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Learn how to specify optional members in a tuple using named tuples and the optional operator in TypeScript.

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Using Optional Tuple Members in TypeScript

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Function Types

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The `void` Type

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Type Checking Maps

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Essential Types And Notations

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Understanding How TypeScript Works in Your IDE

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Introspecting Variables and Declarations in TypeScript

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Hovering Over a Function Call

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TSDoc Comments

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Quick Fix Refactoring

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Automatic Code Formatting with Prettier

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Introducing Union Types in TypeScript

Handling Null Values in TypeScript

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Diving Deeper into Unions and Assignability

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Combining Literal & Union Types

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Literal Type Assignability

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How Big Can a Union Be?

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