I have the following function:
function myFunc(
id: string,
optionalParamOne?: number,
optionalParamTwo?: string
) {
console.log(optionalParamTwo);
}
I would like to call this function by specifying the id as it is required and optionalParamTwo. I don't care about optionalParamOne. I cannot change this function.
How can I call this function with the parameters id and optionalParamTwo without having to specify optionalParamOne?
I could do this:
myFunc('abc', null, 'dog')
But I have many optional parameters in my function signature and I'd rather not specify a value for each.
You must provide some value (even if its undefined) for every ordered parameter before you can provide a value for a higher-indexed parameter.
The common pattern for reducing boilerplate when invoking functions with uninteresting parameters is to curry:
function myFunc (
id: string,
optionalParamOne?: number,
optionalParamTwo?: string
) {
console.log(optionalParamTwo);
}
// Create a parameter-expanding function:
const myParams = (id: string, optionalParamTwo?: string) => [id, undefined, optionalParamTwo] as const;
// ^^^^^^^^^
// Include undefined for the params you don't want to think about when calling the function
myFunc(...myParams('abc', 'dog')); // logs "dog"
// Or just curry it:
const myFuncWithFewerParams = (
id: string,
optionalParamTwo?: string,
) => myFunc(id, undefined, optionalParamTwo);
myFuncWithFewerParams('abc', 'cat'); // logs "cat"
For sliced tuples (addressing partial parameters) in the type system, see this answer.
It's not possible to do so without changing the function. You can write a wrapper around this function with destructuring assignment like so to achieve the desired result:
function myFunc(
id: string,
optionalParamOne?: number,
optionalParamTwo?: string
) {
console.log(optionalParamTwo);
}
interface MyFuncParams {
optionalParamOne?: number,
optionalParamTwo?: string
}
function myFuncWrapper(id: string, { optionalParamOne, optionalParamTwo }: MyFuncParams = {}) {
myFunc(id, optionalParamOne, optionalParamTwo);
}
myFuncWrapper('abc', { optionalParamTwo: 'dog' });