Any and void

There are two essential type-related concepts in TypeScript, each serving distinct purposes in the language. The any type represents a dynamic variable that can hold values of any type, and the void type signifies the absence of a return value in a function. In this topic, we will take a closer look at these TypeScript types and explore their use cases.

Type any

As we know, TypeScript is used to specify types of variables, function parameters, and return values. It prevents bugs and makes code more reliable. But sometimes, during development, there are situations when we still need to override a data type, or the type may not be known at the time we write the application. Then, the any type is used, and we can do whatever we want with the variable. The type any is stated using the keyword any:

let test: any = 100;

Now let's assign a string to this variable:

test = 'hundred';
console.log(test);

After compiling, it logs a string to the console without detecting errors.

Flag noImplicitAny

Enabling the noImplicitAny flag causes an error for all variables whose type is implicitly defined as any. It prohibits the non-explicit use of any in TS, that is, code without a type annotation. The flag can be turned on in the tsconfig.json.

"compilerOptions": {
  /* Type Checking */
  "noImplicitAny": true,
}

function test(arg) {
  return arg;
}

Here, arg implicitly has an any type, so this code won't compile if the flag noImplicitAny is used or the strict mode is enforced.

Type void

The void datatype means the absence of a type, so it can be called the complete opposite of the any type. The primary purpose of the void type is to explicitly indicate that a function or method doesn't have a return value. This data type is specified using the void keyword:

function test(arg: string): void {
  alert(arg);
}

Functions with a return type of void are typically used in cases such as logging to the console, event handlers, and asynchronous operations. In essence, functions with a return type of void are used when you want to encapsulate a series of actions or side effects within a function without expecting it to produce a meaningful return value. They are essential for tasks focused on performing actions rather than computing and returning results.

Conclusion

To sum up, any is a type that can hold values of any type, providing flexibility but sacrificing type safety. It offers maximum flexibility, but sacrifices type safety because TypeScript doesn't perform type checks on any values, so it should be used reasonably. It's often used when working with dynamic or untyped data, migrating from JavaScript, or when you intentionally want to bypass TypeScript's static type checking. To lighten code with implicit type defining, use the noImplicitAny flag

void is used to indicate that a function doesn't return a value, making it clear that the function's purpose is to perform an action or side effect. It's useful for improving code clarity by explicitly stating that a function doesn't produce a value and for catching unintentional usage of a function's return value.