What does the any type do?

TypeScriptJunior~2 min read

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

Explicitly:

javascript

let data: any = 123;

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);
}

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:

You need to temporarily disable type checking (for example, during quick debugging).
You are working with someone else's code or a library without types.
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

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