Fix DOMException when replacing or pushing page history state with a complex object

[iamohd-zz]

When trying to replace a page history state with a complex object, DOMException will be thrown. #775

This PR fixes this issue.

[reinink]

Hmm, this shouldn't ever be necessary, as the page object that's received from a server response is what's saved in history state, and that comes from a JSON response. Meaning, there shouldn't ever be a complex JavaScript object within the page object. I'm honestly sure how that would be possible, without doing something weird/hacky.

[rkyoku]

@reinink could you please remove functions before serializing?

Maybe this is what you call "weird" or "hacky", but I am dynamically adding functions to my object/prop.

Sure it's a different philosophy from using events for everything, but the advantages of this are:

• more intuitive (a mere function call),
• less weird and unnecessary code to communicate from child to parent,
• fewer bugs (e.g. I forgot to attach the handler to the child comp, or misspelled the event name),
• last but not least: it also works BEFORE the child component gets mounted (which doesn't work with events).

Events are golden when props are not passed to components. But when they are, events become irrelevant.

Compare this:

// ParentComp.svelte
export let myobj // retrieved from page props
myobj.onMyEvent = e => {/*do stuff*/}
<ChildComp {myobj} />

// ChildComp.svelte
export let myobj // passed from parent
myobj.onMyEvent()

With this:

// ParentComp.svelte
export let myobj
const onMyEvent = e => {/*do stuff*/}
<ChildComp {myobj} on:myevent={onMyEvent} />

// ChildComp.svelte
import { createEventDispatcher, onMount } from 'svelte'
export let myobj
const dispatch = createEventDispatcher()
onMount(() => {dispatch('myevent', {})})

Sure, you don't save 300 lines of code, but it's still a shorter syntax, more intuitive too, and with better separation of concerns and also less imports, and less error-prone (e.g. "oh fudge, I've been investigating this bug for at least 15 minutes but I just noticed I forgot to attach my event handler" kind of thing).

All you have to do in Inertia is to remove the functions from objects that get serialized, it's not a big deal, and it will give a lot more flexibility to devs.