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crater-webvitals

Web Vitals metrics helpers for crater

moon add mizchi/crater-webvitals@0.19.0
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0.19.0
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README

#Crater Web Vitals

MoonBit helpers for browser-facing Web Vitals signals in Crater.

The public root package currently exposes:

  • CLS helpers: compute_element_shift, compute_total, and LayoutShift
  • LCP helpers: LCPCandidate, LCPTracker, extract_lcp_candidates
  • readiness helpers: ContentReadiness

Use this module when you need metric calculations over Crater layout output without depending on the broader browser shell.

#
ContentReadiness

source
pub(all) struct ContentReadiness {
  lcp_ready : Bool
  lcp_time : Double?
  critical_resources_loaded : Bool
  a11y_ready : Bool
}

Overall content readiness state

#
ContentReadiness::from_lcp_tracker

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fn ContentReadiness::from_lcp_tracker(tracker : LCPTracker, a11y_ready : Bool) -> ContentReadiness

Create readiness state from LCP tracker

#
ContentReadiness::is_interaction_ready

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fn ContentReadiness::is_interaction_ready(self : ContentReadiness) -> Bool

Check if content is ready for interaction

#
ContentReadiness::new

source

#
LCPCandidate

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pub(all) struct LCPCandidate {
  element_id : String
  element_type : LCPElementType
  size : Double
  x : Double
  y : Double
  width : Double
  height : Double
  resource_loaded : Bool
  render_time : Double?
  load_time : Double?
}

A candidate element for Largest Contentful Paint

#
LCPCandidate::get_lcp_time

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fn LCPCandidate::get_lcp_time(self : LCPCandidate) -> Double?

Get the LCP time (load_time for images, render_time for text)

#
LCPCandidate::is_rendered

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fn LCPCandidate::is_rendered(self : LCPCandidate) -> Bool

Check if this candidate is fully rendered (resource loaded if applicable)

#
LCPCandidate::new

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fn LCPCandidate::new(element_id : String, element_type : LCPElementType, x : Double, y : Double, width : Double, height : Double) -> LCPCandidate

#
LCPCandidate::with_load_time

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fn LCPCandidate::with_load_time(self : LCPCandidate, time : Double) -> LCPCandidate

#
LCPCandidate::with_render_time

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fn LCPCandidate::with_render_time(self : LCPCandidate, time : Double) -> LCPCandidate

#
LCPCandidate::with_resource_loaded

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fn LCPCandidate::with_resource_loaded(self : LCPCandidate, loaded : Bool) -> LCPCandidate

#
LCPElementType

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pub(all) enum LCPElementType {
  Image(src~ : String)
  BackgroundImage(url~ : String)
  Video(poster~ : String?)
  TextBlock
} derive(Eq, 
Debug)

Types of elements that can be LCP candidates Per spec: , inside , poster, element with background-image, text block elements

#
LCPTracker

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pub struct LCPTracker {
  candidates : Array[LCPCandidate]
  current_lcp : LCPCandidate?
  finalized : Bool
  viewport_width : Double
  viewport_height : Double
}

Tracks LCP candidates and determines the final LCP element

#
LCPTracker::add_candidate

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fn LCPTracker::add_candidate(self : LCPTracker, candidate : LCPCandidate) -> Unit

Add a new LCP candidate

#
LCPTracker::finalize

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fn LCPTracker::finalize(self : LCPTracker) -> Unit

Finalize LCP (called on first user input)

#
LCPTracker::get_lcp

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fn LCPTracker::get_lcp(self : LCPTracker) -> LCPCandidate?

Get the current LCP candidate

#
LCPTracker::get_lcp_time

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fn LCPTracker::get_lcp_time(self : LCPTracker) -> Double?

Get LCP time in milliseconds

#
LCPTracker::is_finalized

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fn LCPTracker::is_finalized(self : LCPTracker) -> Bool

Check if LCP is finalized

#
LCPTracker::is_lcp_ready

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fn LCPTracker::is_lcp_ready(self : LCPTracker) -> Bool

Check if LCP is ready (largest element fully rendered)

#
LCPTracker::new

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fn LCPTracker::new(viewport_width : Double, viewport_height : Double) -> LCPTracker

#
LCPTracker::on_element_rendered

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fn LCPTracker::on_element_rendered(self : LCPTracker, element_id : String, render_time : Double) -> Unit

Update render time for an element

#
LCPTracker::on_resource_loaded

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fn LCPTracker::on_resource_loaded(self : LCPTracker, element_id : String, load_time : Double) -> Unit

Update resource load status for an element

#
LayoutShift

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pub(all) struct LayoutShift {
  impact_fraction : Double
  distance_fraction : Double
  score : Double
}

Result of CLS calculation
impl Show for LayoutShift

#
compute_element_shift

source

Calculate layout shift between two bounding rects viewport: the viewport size for normalization

#
compute_total

source

Calculate total CLS score for multiple elements

#
extract_lcp_candidates

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fn[T : 
LayoutView] extract_lcp_candidates(root : T, viewport_width : Double, viewport_height : Double) -> Array[LCPCandidate]

Extract LCP candidates from any layout view tree root.

The function is generic over the layout impl: pass the root of a concrete tree (e.g. LayoutTree::root from crater-layout/tree) or any other type that implements @view.LayoutView.

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