Forked from anniesullie/LargestContentfulPaintBookmarklet.js
Created
May 19, 2021 14:56
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/** | |
* A bookmarklet for viewing the largest contentful paint in a page. | |
* Will show each LCP after the bookmarklet is clicked. | |
* | |
* To install: | |
* 1. Copy the code starting from the line beginning `javascript:` | |
* 2. Add a new bookmark in Chrome, and paste the code in as the URL. | |
**/ | |
javascript:(function(){ | |
try { | |
const canvas = document.createElement('canvas'); | |
canvas.style.width = '100%'; | |
canvas.style.height = '100%'; | |
canvas.width = window.innerWidth; | |
canvas.height = window.innerHeight; | |
canvas.style.position = 'absolute'; | |
canvas.style.left = 0; | |
canvas.style.top = 0; | |
canvas.style.zIndex = 100000; | |
canvas.style.pointerEvents = 'none'; | |
document.body.appendChild(canvas); | |
const context = canvas.getContext('2d'); | |
const po = new PerformanceObserver((list) => { | |
for (const entry of list.getEntries()) { | |
let rect = entry.element.getBoundingClientRect(); | |
context.clearRect(0, 0, canvas.width, canvas.height); | |
context.strokeStyle = 'red'; | |
context.strokeRect(rect.x, | |
rect.y, | |
rect.width, | |
rect.height); | |
} | |
}); | |
po.observe({type: 'largest-contentful-paint', buffered: true}); | |
} catch (e) { | |
} | |
})(); |
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