tw-image-metrics

Scrapes a page to gather performance metrics about loaded images.

Usage

You must pass a valid window object for the page you wish to scrape.

var imageMetrics = require('tw-image-metrics');
var data = imageMetrics(window);

Optionally, you can also pass an array of filetypes to filter by.

var pngsOnly = imageMetrics(window, ['png']);

Result

tw-image-metrics returns an array of objects with performance data for each image.

[{
  url: "https://foo.bar/image.png",
  type: "png",
  size: 123.45,
  loadTime: 250,
  width: 1024,
  height: 768,
  from: "css"
}]

url: the full URL of the image.

type: The filetype of the image.

size: The filesize of the image (in kilobytes).

loadTime: The time it took to load the image (in milliseconds).

width: The width of the image (in pixels).

height: The height of the image (in pixels).

from: The source of the image. Typically, this is img for images loaded from HTML, and css for images loaded from CSS.

Notes

tw-image-metrics may return 0 for the size property if the image is loaded from the cache. Make sure your cache is clear before calling this function.