How to get Argument Types from Function in TypeScript ?

In TypeScript, the Parameters utility type allows you to extract the types of a function’s parameters. This is particularly useful when you want to work with the types of arguments dynamically, enabling functions that operate on any function’s parameter types. In this article, we are going to see how to get argument types from functions in Typescript.

Syntax:

function exampleFunction(arg1: string, arg2: number, arg3: boolean): void {
  // Function body
}
// Use the Parameters utility type to get the argument types
type ArgumentTypes = Parameters<typeof exampleFunction>;
function logArgumentTypes(...args: ArgumentTypes): void {
  args.forEach(arg => console.log(typeof arg));
}

Approach

• Start by defining the function from which you want to extract the argument types.
• Utilize the Parameters utility type to extract the argument types.
• Design a function to log the types of arguments.
• Apply the extracted types in your logging function.

Example: In this example, the logArgumentTypes function uses the typeof operator to log the type of each argument.

Javascript

// Define a sample function
function exampleFunction(arg1: string, arg2:
    number, arg3: boolean): void {
    // Function body
}

type ArgumentTypes = Parameters<typeof exampleFunction>;

function logArgumentTypes(...args: ArgumentTypes):
    void {
    // Log the type of each argument
    args.forEach(arg => console.log(typeof arg));
}

const args: ArgumentTypes = ['Geeks', 22, true];
logArgumentTypes(...args);

Output:

string
number
boolean

Example 2: In this example, the printNumberTypes function now correctly logs the type of each number using the typeof operator.

Javascript

function addNumbers(a: number,
    b: number): number {
    return a + b;
}

type AddNumbersArgs = Parameters<typeof addNumbers>;

function printNumberTypes(...numbers:
    AddNumbersArgs): void {
    numbers.forEach(num => console.log(typeof num));
}

const result: AddNumbersArgs = [10, 20];
printNumberTypes(...result);

Output:

number
number