Objects.hasFunction()

added in 0.2.0 • updated in 0.4.0 • last revisions

Syntax

function hasFunction(source: unknown, functionName: string | number | symbol, argumentCount?: number): boolean

Checks if an object contains a function by the specified name and number of arguments.

Parameters
`source`	The value to check for presence of the function. Accepts any type.
`functionName`	The name of the function to check for.
`argumentCount` Optional	If passed, `hasFunction()` returns `false` if the function does not accept this exact number of arguments.

Example

import { Objects } from 'potence';

const object: unknown = { ... };

if (Objects.hasFunction(object, 'doSomething', 2)) {
    object.doSomething('with', 'me');  // no error
}

Remarks

This function is a type guard. When used in an if condition, this function will therefore allow you to call source[functionName]() without any TypeScript errors.

Note that, because it is not possible to perform a runtime check for the type of parameters or the return type, both of these will be typed as unknown. In other words: you will be able to pass an arbitrary number of arguments of any type to the function, but to use the function’s return type you’ll have to perform another type check.

This function is particularly useful when defining custom type guards.

Compare with Objects.hasProperty(), which can check for the presence of properties of other types.

Note: For the sake of simplicity, the above function signature is an abridged version of the function’s real signature. To ensure proper TypeScript typing—especially in regards to the return type—a slightly more complex function signature is needed than what is shown here.