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

victorpolko

var simpleUniq = function(array) {
  return array.reduce(function(prev, curr, index, arr) {
    if (prev.indexOf(curr) === -1) prev.push(curr);
    return prev;
  }, []);
}

victorpolko

var duplicates = function(array) {
  var iteratee = array.slice(0);
  var seen = [];
  
  return array.filter(function(element) {
    iteratee.shift();
    if (seen.indexOf(element) !== -1) return false;
    
    var hit = iteratee.indexOf(element) !== -1;
    if (hit && seen.indexOf(element) === -1) seen.push(element);