Is there a way to create destructured parameters with optional typing in TypeScript?
For instance, I am trying to make the following function callable without requiring any parameters.
const func = ({param}: {param?: boolean}) => {};
Currently, TypeScript is throwing an error stating that a parameter is missing.
It seems like you're concerned about the error displayed below:
const fooBad = ({ bar }?: { bar?: boolean }) => {}; // error!
// ┌──────────> ~~~~~~~~~~~~~~~~~~~~~~~~~~~
// A binding pattern parameter cannot be optional in an implementation signature.
This error is understandable because you can't destructure undefined. In TypeScript, one way to work around this is by using a default function parameter. By doing so, you treat it as an optional parameter when calling the function and set a value if it's undefined on the implementation side.
If your intention is to have bar as undefined when someone calls foo(), then you can pass either {bar: undefined} or simply {} since bar is optional:
const foo = ({ bar }: { bar?: boolean } = {}) => {
console.log(bar);
};
I included console.log(bar) so you can see the output for different function calls:
foo(); // undefined
foo({}); // undefined
foo({bar: true}); // true
Seems like everything is working correctly. Good luck with your coding endeavors!
In the realm of JavaScript, it is not feasible as it does not function in that context either. For instance, consider this snippet of JS:
const foo = ({bar}) => {
...
};
foo({ bar: 123 }); // runs successfully
foo(); // throws an error
Attempting to call foo sans an object parameter will yield an exception like so:
Uncaught TypeError: Cannot destructure property `bar` of 'undefined' or 'null'.
This occurs due to the similarity between the aforementioned function implementation and this equivalent representation:
const foo = (arg1) => {
let bar = arg1.bar;
};
foo();
The resulting exception would be nearly identical because arg1.bar seeks to access a property on an object that is deemed undefined.
To put it succinctly, at runtime, JavaScript lacks recognition of "optional" parameters, leading TypeScript to follow suit.
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