Understanding TypeScript's any and unknown Types: When to Use Each


TypeScript, a powerful superset of JavaScript, revolutionizes the world of web development by incorporating strong typing, allowing developers to identify and rectify errors at an early stage, resulting in the creation of more robust and dependable code.

Among its plethora of features, TypeScript offers developers the flexibility of utilizing two fundamental types: any​ and unknown​. While both types provide versatility, they are designed for specific purposes, and having a clear understanding of when to apply each is crucial for developing maintainable and bug-free code.

The "any" Type:

  • The any​ type in TypeScript is the most flexible type.
  • Variables of type any​ in TypeScript have the ability to store values of any type, evading TypeScript's type validation.
  • It is commonly used when converting JavaScript code to TypeScript or when handling different data types.
  • However, the use of any​ sacrifices type safety and may lead to runtime errors if not used with caution.
  • Example: let data: any = 10;​​

The "unknown" Type:

  • Introduced in TypeScript 3.0, the unknown​ type represents values whose types are not known at compile time.
  • Unlike any, variables of type unknown​ still enforce type checking, preventing unintended type conversions and ensuring type safety.
  • Before manipulating values of unknown​ types, developers should identify the specific type to ensure accurate operations.
  • It becomes especially advantageous when working with external data sources, such as responses from APIs, where the specific data type may not be clearly defined or known in advance, requiring flexibility in handling the information.
  • Example: let userInput: unknown = 'Hello';

In TypeScript, the unknown type is a type that represents values that we do not yet know the type of. It is similar to the any type, but with some important differences. When a value is of type unknown, TypeScript requires you to perform some type of type-checking or type assertion before you can safely use that value.

Here is an example of how you can use the unknown type in TypeScript:


function getValue(): unknown {
return "Hello, TypeScript!";
const value: unknown = getValue();
if (typeof value === "string") {
} else {
console.log("Value is not a string.");

In this example, the getValue function returns a value of type unknown, and we need to check if it is a string before we can safely call toUpperCase on it.

When to Use Each Type:

1. `unknown`:
  • Use unknown​ when you want to represent a value whose type is not known at compile time.
  • It is safer than using any because you must perform some type of checking before you can use the value.
  • You need to narrow down the type of unknown before you can perform operations on it.
  • Prefer using unknown​ instead of any for improved type safety and more robust error handling.
2. `any`:
  • Use `any` when you want to opt out of type checking and have a variable that can hold any type of value.
  • It is less restrictive than unknown as you can perform any operation on a variable of type any without type checking.
  • Using any can lead to potential runtime errors if the variable is not used carefully.
  • It is advisable to utilize the any​ type in situations involving legacy code, when you are working with JavaScript libraries, or when you do not need to specify the exact type of a variable.

In general, it is recommended to use unknown over any when you are unsure about the type of a value, as it provides more type safety. Use any only when you need to work with values of unknown or dynamic types without type checking.

Best Practices:

  • Minimize the use of any​ to specific scenarios where its flexibility is truly necessary.
  • Always aim to narrow down variables of type unknown​ to a known type before performing operations on them.
  • Leverage TypeScript's type guards, such as typeof​, instanceof​, and user-defined type predicates, to safely handle unknown​ types.
  • Document and communicate the rationale behind using any​ or unknown​ types in your codebase to facilitate collaboration and understanding among team members.


When delving into the realm of TypeScript, developers encounter the any​ and unknown​ types, which prove to be indispensable in handling data types that are subject to change and uncertainty. 

While the any​ type offers unparalleled flexibility by completely bypassing type checks, the unknown​ type strikes a balance by maintaining type safety while allowing developers to work with values of uncertain types. 

By gaining a deep understanding of the distinctions between these two types and adhering to established best practices, developers can craft more resilient and maintainable TypeScript code, thereby ensuring enhanced reliability and scalability in their projects.

Understanding TypeScript's any and unknown Types: When to Use Each
Ram Krishna April 7, 2024
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