Default properties in parent component default to "undefined" when omitted with spread

[lud]

Simple demo here : https://svelte.dev/repl/d0476b3598e648cfbe38922617a8798c?version=3.5.3

Basically, if you have an object that is used as spread props for a child component, and you overwrite the variable with a new object with different keys, the keys that were present and are missing takes precedence as undefined over the child component default values.

[btk5h]

Is this a bug? This behavior makes sense to me since the code inside the script block is only executed once. export let title = 'No title' is more of an initial value rather than a default/fallback value.

You could use the || operator to provide a fallback value if one of the props becomes undefined after the component is mounted.

[lud]

I see. I may have misiterpreted how things work here. Is there a simple way to force a nested component to recreate ?

[alfredomariamilano]

That's expected vanilla JS behaviour. Either you use subProps.text = 'Some text' or subProps = { ...subProps, text: 'Some text' }.

[lud]

The combination of $: and || is good enough :)