@ -490,6 +490,23 @@ let { a, b, c, ...everythingElse }: MyProps = $props();
>
> ...TypeScript [widens the type](https://www.typescriptlang.org/play?#code/CYUwxgNghgTiAEAzArgOzAFwJYHtXwBIAHGHIgZwB4AVeAXnilQE8A+ACgEoAueagbgBQgiCAzwA3vAAe9eABYATPAC+c4qQqUp03uQwwsqAOaqOnIfCsB6a-AB6AfiA) of `x` to be `string | number`, instead of erroring.
If you're using JavaScript, you can declare the prop types using JSDoc:
```js
/** @type {{ x: string }} */
let { x } = $props();
// or use @typedef if you want to document the properties:
/**
* @typedef {Object} MyProps
* @property {string} y Some documentation
*/
/** @type {MyProps} */
let { y } = $props();
```
By default props are treated as readonly, meaning reassignments will not propagate upwards and mutations will result in a warning at runtime in development mode. You will also get a runtime error when trying to `bind:` to a readonly prop in a parent component. To declare props as bindable, use [`$bindable()`](#$bindable).