fix(bindEvent): escape payload correctly

[eunjae-lee]

Summary

This PR updates the way we serialize & deserialize payloads for bindEvent. It's internal and users never got to deserialize by themselves, so it's not a breaking change.

Details

Since "add hits and attributes to InsightsEvent" PR, bindEvent method now serializes hits as well. And hits can contain special characters unlike the payloads that we used to have in insights middleware.

For example,

btoa('™')
> Uncaught DOMException: String contains an invalid character

but

btoa(encodeURIComponent('™'))
> "JUUyJTg0JUEy"

decodeURIComponent(atob("JUUyJTg0JUEy"))
> "™"

A minor concern

It's actually not about this PR, but about the previous "add hits and attributes to InsightsEvent" PR.
Now that we expose hits to InsightsEvent, its payload is much bigger than before. It's going to bloat the DOM output.
When they have templates like

<button
  type="button"
  ${bindEvent('click', hit, 'Favorite')}
>
 ...
</button>

If they don't pass the whole hit object, and pass only a subset of it, it will reduce the size. What do you think?

[codesandbox-ci]

This pull request is automatically built and testable in CodeSandbox.

To see build info of the built libraries, click here or the icon next to each commit SHA.

Latest deployment of this branch, based on commit 3f29d79:

Sandbox	Source
InstantSearch.js	Configuration

[Haroenv]

reasonable fix!

[eunjae-lee]

reasonable fix!

You also think the A minor concern part is okay?

[Haroenv]

it's probably not really an issue IMO, although a subset was already set with objectIDs, which you said was insufficient for segment

[eunjae-lee]

it's probably not really an issue IMO, although a subset was already set with objectIDs, which you said was insufficient for segment

What I meant by a subset was to pass an object made from hit with some properties omitted like, for example, image_url, description, ... that won't be used in the insights middleware.

It could bloat the html size and might be an issue in case of SSR. Even if so, they can omit some properties to avoid the issue.