Suggest an edit

Improve this article

Refine the answer for “What does the any type do?”. Your changes go to moderation before they’re published.

Approval required

Content

What you’re changing

Title (EN)

Short answer (EN)

Shown above the full answer for quick recall.

Answer (EN)

### What the `any` type does in TypeScript

The `any` type in TypeScript literally means:

> "**Any type** - turn off type checking here completely."

That is, when a variable has type `any`, **TypeScript stops controlling** anything that happens to it:
what values are assigned, what methods are called, what properties are read - **everything is allowed**.

---

### Example: behavior of the `any` type

```javascript
let value: any = 10;

value = "text";
value = { a: 1 };
value = [1, 2, 3];
value = true;

// TypeScript does not complain, even if the logic makes no sense
value.toUpperCase();     // compiles (even if it is not a string)
value.nonexistentField;  // compiles (may be undefined)
value();                 // compiles (even if it is not a function)
```

---

### When TypeScript assigns the `any` type

1. **Explicitly:**

```javascript
  let data: any = 123;
  ```
2. **Implicitly**, if you did not specify a type and **TypeScript cannot infer it itself** (and `noImplicitAny` is off):

```javascript
  function log(message) { // message: any (by default)
    console.log(message);
  }
  ```
3. **After parsing unknown data without an annotation:**

```javascript
  const obj = JSON.parse("{}"); // type: any
  ```

---

### Why `any` is dangerous

The `any` type **disables the type system** for a particular piece of code.
Because of this, you can get **errors only at runtime**, not at compile time.

Example:

```javascript
let data: any = "Hello";

console.log(data.toFixed(2)); // Runtime error - data is a string
```

TypeScript will not warn you, because `any` says:

> "I trust the programmer - do not check me."

---

### Difference between `any` and `unknown`

| Property | `any` | `unknown` |
|---|---|---|
| Any values can be assigned | Yes | Yes |
| Any methods can be called and properties accessed | Yes | No (only after a check) |
| Type checking | Disabled | Strict |
| Safety | Low | High |
| Used for | Fast development, prototypes | Unknown but potentially unsafe data |

Example:

```javascript
let a: any = "text";
a.toFixed(2); // compiles, but throws an error

let b: unknown = "text";
// b.toFixed(2); // compile-time error - safe
```

---

### When `any` can be used

Using `any` **is acceptable, but with caution**, in situations where:

1. You need to **temporarily** disable type checking (for example, during quick debugging).
2. You are working with **someone else's code or a library without types**.
3. You are writing a **wrapper around an external API** where the types are not yet known.

Example:

```javascript
// Temporary disabling of typing
let response: any;
try {
  response = JSON.parse(dataFromServer);
} catch {
  response = null;
}
```

---

### When `any` should NOT be used

- In **production code**, where reliability matters.
- In **large projects** - `any` destroys the type system and makes refactoring dangerous.
- In **libraries** - it kills autocomplete and type checking for users.

---

### Alternative to `any`

Use:

- `unknown` -> if the type is unknown, but you want to **preserve safety**.
- `as Type` -> if you know the type for sure, but TS cannot infer it.
- `Record<string, unknown>` -> if it is an object, but the structure is unknown.

---

### Summary

| Property | Description |
|---|---|
| Type | Primitive utility type |
| Allows any operations | Yes |
| Type checking | Disabled |
| Safety | Very low |
| Main use | Temporary, when working with unpredictable data |
| Alternative | `unknown`, `as`, an explicit type description |

Markdown · drag & drop images · ⌘B / ⌘I shortcuts590 words

For the reviewer

Note to the moderator (optional)

Visible only to the moderator. Helps review go faster.