Run results for: addFunction vs classList (multiple)

Run details:

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/86.0.4240.111 Safari/537.36 Edg/86.0.622.51

Browser: Chrome 86

Operating system: Windows

Device Platform: Desktop

Date tested: 3 years ago

Test name	Executions per second
addClass function	275.9 Ops/sec
classList	278.6 Ops/sec
classList multiple params	458.3 Ops/sec
addClass function with classList	255.3 Ops/sec

HTML Preparation code:

<div id="foo"></div>

Script Preparation code:

function addClass(el, classNames)
{
  if (!classNames) { return; }
 
        if (!Object.prototype.toString.call(classNames) === "[object Array]")
        {
            classNames = classNames.split(' ');
        }
        var className = el.getAttribute("class") || "";
 
        var i, classMap = {}, currentClasses = [], length;
 
        if (className !== null)
        {
            currentClasses = className.split(" ");
 
            length = currentClasses.length;
            for (i = 0; i < length; i++)
            {
                if (currentClasses[i] !== "")
                {
                    classMap[currentClasses[i]] = "";
                }
            }
        }
 
        var changed = false, trimmedName;
        var newAdded = [];
        length = classNames.length;
        for (i = 0; i < length; i++)
        {
            trimmedName = classNames[i].trim();
            if ((trimmedName.length > 0) && !(trimmedName in classMap))
            {
                currentClasses.push(trimmedName);
                newAdded.push(trimmedName);
                classMap[trimmedName] = "";
                changed = true;
            }
        }
 
        if (changed)
        {
            el.setAttribute("class", currentClasses.join(" ").trim());
        }
 
        return newAdded;
}

function addClass2(el, classNames)
{
  if (!classNames) { return; }
 
        if (!Object.prototype.toString.call(classNames) === "[object Array]")
        {
            classNames = classNames.split(' ');
        }
        var className = el.getAttribute("class") || "";
  
        var trimmedName;
        var newAdded = [];
        var length = classNames.length;
        var list = el.classList;
        for (i = 0; i < length; i++)
        {
            trimmedName = classNames[i].trim();
            list.add(trimmedName);
        }
  
        return newAdded;
}

Tests:

addClass function
var i = 1000; while (i--) { var element = document.getElementById("foo"); element.className = "bar2"; addClass(element, ["bar", "bar2", "bar3"]); }
classList
var i = 1000; while (i--) { var element = document.getElementById("foo"); element.className = "bar2"; var list = element.classList; list.add("bar"); list.add("bar2"); list.add("bar3"); }
classList multiple params
var i = 1000; while (i--) { var element = document.getElementById("foo"); element.className = "bar2"; element.classList.add("bar", "bar2", "bar3"); }
addClass function with classList
var i = 1000; while (i--) { var element = document.getElementById("foo"); element.className = "bar2"; addClass2(element, ["bar", "bar2", "bar3"]); }

Run results for: addFunction vs classList (multiple)

addClass function

classList

classList multiple params

addClass function with classList