javascript document.getElementsByClassName compatibility with IE

Question

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.

Answer 1

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

Answer 2

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
);

Answer 3

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;
    }
}

Answer 4

IE8:

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

Answer 5

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

Answer 6

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.