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

ekarulf

def etree(packages=('lxml.etree', 'xml.etree.cElementTree',
                    'cElementTree', 'elementtree.ElementTree')):
    for pkg_name in packages:
        try:
            pkg = __import__(pkg_name)
        except ImportError:
            continue
        else:
            for subpkg_name in pkg_name.split('.')[1:]:  # skip the base package
                pkg = getattr(pkg, subpkg_name)