paulirish

What forces layout / reflow

All of the below properties or methods, when requested/called in JavaScript, will trigger the browser to synchronously calculate the style and layout*. This is also called reflow or layout thrashing, and is common performance bottleneck.

Generally, all APIs that synchronously provide layout metrics will trigger forced reflow / layout. Read on for additional cases and details.

Element APIs

Getting box metrics

• elem.offsetLeft, elem.offsetTop, elem.offsetWidth, elem.offsetHeight, elem.offsetParent

lygaret

define(function(require) {
    var React = require('react');

    var paramRegex  = /__(\d)+/;
    var parser      = new DOMParser();
    var errorDoc    = parser.parseFromString('INVALID', 'text/xml');
    var errorNs     = errorDoc.getElementsByTagName("parsererror")[0].namespaceURI;

    // turns the array of string parts into a DOM
    // throws if the result is an invalid XML document.

addyosmani

Update May 2017

Eric Bidelman has documented some of the common workflows possible with headless Chrome over in https://developers.google.com/web/updates/2017/04/headless-chrome.

Update

If you're looking at this in 2016 and beyond, I strongly recommend investigating real headless Chrome: https://chromium.googlesource.com/chromium/src/+/lkgr/headless/README.md

Windows and Mac users might find using Justin Ribeiro's Docker setup useful here while full support for these platforms is being worked out.