Wrong OCI picked up if scroll happens before beacon fires - Beacon side

[Miraeld]

Describe the bug
Wrong OCI will be picked up if the page is scrolled and the beacon script is fired after.
This issue will handle the rocket-scripts side.

Reproduce the problem

• Use - https://gist.github.com/DahmaniAdame/bd58d4be051f5995aa2318d341eb342a
• Scroll to the last image
• Hit refresh while making sure the beacon runs
• See the LCP image will be related to the current viewport

Identify the root cause

The issue is that the OCI data is collected incorrectly if the user scrolls before the beacon fires. This can happen when the user scrolls on mobile or refreshes the page away from the fold.

Scope a solution

To solve the issue, we must create a new function in BeaconManager.js:

  _isPageScrolled() {
        return window.pageYOffset > 0 || document.documentElement.scrollTop > 0;
    }

and finalize the process of beacon if it returns true:

    async init() {
        this.scriptTimer = new Date();
        if (!await this._isValidPreconditions()) {
            this._finalize();
            return;
        }

        if (this._isPageScrolled()) {
            this.logger.logMessage('Bailing out because the page has been scrolled');
            this._finalize();
            return;
        }
// ...

Development steps:

• Create the function _isPageScrolled()
• Modify init function to finalize if the newly added function returns true.

Effort estimation:

XS

Is a refactor needed in that part of the codebase?

No