Node.js "No overload matches this call." error with TypeScript

Matthew C.

—August 15, 2024

The ProblemThe Problem

When calling a TypeScript function, you may get the following error:

No overload matches this call.

This error occurs when a function or method is called with arguments that don’t match any of the function’s overload signatures.

The SolutionThe Solution

Ensure that the arguments and types of your function call match one of the function’s overload signatures.

In TypeScript, you can use overload signatures to specify a function that can be called with a variable number of arguments, argument types, and return types.

Each overload signature defines the parameter and return types of the function. They don’t have a function body. You also need to define an implementation signature that has a function body. The types of the implementation signature functions should match all of the types of the overload signatures.

// Overload signatures
function combine(a: string, b: string): string;
function combine(a: string[], b: string[]): string[];

// Implementation signature
function combine(a: unknown, b: unknown): unknown {
  if (Array.isArray(a) && Array.isArray(b)) {
    return [...a, ...b];
  } else if (typeof a === "string" && typeof b === "string") {
    return a + b;
  }
  throw new Error("Invalid arguments");
}

When calling the function, call it using the types of one of the overload signatures. If you call the function using arguments that don’t match one of the overload signatures, you’ll get the No overload matches this call error.

For example, you could call the combine function, defined above, with a number as its first argument, as follows:

console.log(combine(1 , "world!"));

If you called the function above, you would get the following error:

No overload matches this call.
Overload 1 of 2, '(a: string, b: string): string', gave the following error.
Argument of type 'number' is not assignable to parameter of type 'string'.
Overload 2 of 2, '(a: string[], b: string[]): string[]', gave the following error.
Argument of type 'number' is not assignable to parameter of type 'string[]'.(2769)

If, however, you called the combine function with two “string” arguments of the type “string”, you wouldn’t get any errors:

console.log(combine("Hello, ", "world!"));

Function overloads should only be used when the function signature is complex:

function combine(
  a: string | string[],
  b: string | string[]
): string | string[] {
  if (Array.isArray(a) && Array.isArray(b)) {
    return [...a, ...b];
  } else if (typeof a === "string" && typeof b === "string") {
    return a + b;
  }
  throw new Error("Invalid arguments");
}

You should rather use union types when possible.

View TypeScript Playground DemosView TypeScript Playground Demos

You can see live demos of the examples in the TypeScript Playground:

• TypeScript Playground demo of the function calling error

• TypeScript Playground demo of the correct function call

• TypeScript Playground demo of the function overload

Learn MoreLearn More

To learn more about function overloads, take a look at the TypeScript docs.