javascript document.getElementsByClassName compatibility with IE

What is the best method to retrieve an array of elements that have a certain class?

I would use document.getElementsByClassName but IE does not support it.

So I tried Jonathan Snook's solution:

function getElementsByClassName(node, classname) {
    var a = [];
    var re = new RegExp('(^| )'+classname+'( |$)');
    var els = node.getElementsByTagName("*");
    for(var i=0,j=els.length; i<j; i++)
        if(re.test(els[i].className))a.push(els[i]);
    return a;
}
var tabs = document.getElementsByClassName(document.body,'tab');

...but IE still says:

> Object doesn't support this property or method

Any ideas, better methods, bug fixes?

I would prefer not to use any solutions involving jQuery or other "bulky javascript".

Update:

I got it to work!

As @joe mentioned the function is not a method of document.

So the working code would look like this:

function getElementsByClassName(node, classname) {
    var a = [];
    var re = new RegExp('(^| )'+classname+'( |$)');
    var els = node.getElementsByTagName("*");
    for(var i=0,j=els.length; i<j; i++)
        if(re.test(els[i].className))a.push(els[i]);
    return a;
}
var tabs = getElementsByClassName(document.body,'tab');

...Also if you only need IE8+ support then this will work:

if(!document.getElementsByClassName) {
	document.getElementsByClassName = function(className) {
		return this.querySelectorAll("." + className);
	};
	Element.prototype.getElementsByClassName = document.getElementsByClassName;
}

Use it just like normal:

var tabs = document.getElementsByClassName('tab');

It's not a method of document:

function getElementsByClassName(node, classname) {
    var a = [];
    var re = new RegExp('(^| )'+classname+'( |$)');
    var els = node.getElementsByTagName("*");
    for(var i=0,j=els.length; i<j; i++)
        if(re.test(els[i].className))a.push(els[i]);
    return a;
}

tabs = getElementsByClassName(document.body,'tab');  // no document

you may create the function for older browsers

if (typeof document.getElementsByClassName!='function') {
	document.getElementsByClassName = function() {
		var elms = document.getElementsByTagName('*');
		var ei = new Array();
		for (i=0;i<elms.length;i++) {
			if (elms[i].getAttribute('class')) {
				ecl = elms[i].getAttribute('class').split(' ');
				for (j=0;j<ecl.length;j++) {
					if (ecl[j].toLowerCase() == arguments[0].toLowerCase()) {
						ei.push(elms[i]);
					}
				}
			} else if (elms[i].className) {
				ecl = elms[i].className.split(' ');
				for (j=0;j<ecl.length;j++) {
					if (ecl[j].toLowerCase() == arguments[0].toLowerCase()) {
						ei.push(elms[i]);
					}
				}
			}
		}
		return ei;
	}
}

function getElementsByClassName(className) {
if (document.getElementsByClassName) { 
  return document.getElementsByClassName(className); }
else { return document.querySelectorAll('.' + className); } }

Pretty sure this is the same as Leonid's function but this uses document.getElementsByClassName when it can.

You can't really replicate getElementsByClassName, because it returns a nodeList, and so its value is live, and updates with the document.

You can return a static Array of elements who share the same classnames- but it won't 'know'when the document changes.

(It won't take too many of these kind of things to make a library look svelte...)

function getArrayByClassNames(classes, pa){
	if(!pa) pa= document;
	var C= [], G;
	if(pa.getElementsByClassName){
		G= pa.getElementsByClassName(classes);
		for(var i= 0, L= G.length; i<L; i++){
			C[i]= G[i];
		}
	}
	else{
		classes= classes.split(/\s+/);
		var who, cL= classes.length,
		cn, G= pa.getElementsByTagName('*'), L= G.length;
		for(var i= 0; i<cL; i++){
			classes[i]= RegExp('\\b'+classes[i]+'\\b');
		}
		classnameLoop:
		while(L){
			who= G[--L];
			cn= who.className;
			if(cn){
				for(var i= 0; i<cL; i++){
					if(classes[i].test(cn)== false) {
						continue classnameLoop;
					}
				}
				C.push(who);
			}
		}
	}
	return C;
}

//Example

var A= getArrayByClassNames('sideBar local')

IE8:

document.getElementsByClassName = function (className) {
    return document.querySelectorAll('.' + className)
}

function _getClass(whatEverClasNameYouWant){
var a=document.getElementsByTagName('*');
   for(b in a){
      if((' '+a[b].className+' ').indexOf(' '+whatEverClasNameYouWant+' ')>-1){
      return a[b];
      }
   }
}

I just want to improve querySelectorAll fallback for IE8.

Like others answered, the simple way is adding the function to Element.prototype with

this.querySelectorAll('.' + className);

But there are some problems:

• It doesn't work with untrimmed strings (at the beginning).
• It doesn't work with multiple classes.
• It doesn't work with "strange" class characters (/, $, *, etc.)
• It doesn't work with classes which begin with a digit (invalid identifiers)

That means there should be some "fixing", for example:

"abcd"     ->  ".abcd"
"a   b cd" ->  ".a.b.cd"
"   a b  " ->  ".a.b  "
"a/b$c d"  ->  ".a\/b\$c.d"
"1234"     ->  ".\000031234"

Code:

this.querySelectorAll(className
    .replace(/(?=[^ \w])/g, '\\')   // Escape non-word characters
    .replace(/\b\d/g, '\\00003$&')  // Escape digits at the beginning
    .replace(/(^| +)(?!$| )/g, '.') // Add "." before classes, removing spaces
);