zmofei

function add(a, b) {
    var res = '',
        c = 0
    a = a.split('')
    b = b.split('')
    while (a.length || b.length || c) {
        c += ~~a.pop() + ~~b.pop()
        res = c % 10 + res
        c = c > 9
    }

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