How to get all elements by class name?

How do you get all elements by class name using pure JavaScript? Analogous to $('.class') in JQuery?

document.getElementsByClassName(klass)

Be aware that some engines (particularly the older browsers) don't have it. You might consider using a shim, if that's the case. It will be slow, and iterate over the whole document, but it will work.

EDIT several years later: You can get the same result using document.querySelectorAll('.klass'), which doesn't seem like much, but the latter allows queries on any CSS selector, which makes it much more flexible, in case "get all elements by class name" is just a step in what you are really trying to do, and is the vanilla JS answer to jQuery's $('.class').

A Simple and an easy way

var cusid_ele = document.getElementsByClassName('custid');
for (var i = 0; i < cusid_ele.length; ++i) {
    var item = cusid_ele[i];  
    item.innerHTML = 'this is value';
}

document.getElementsByClassName('your class');  

or you can build your classname like this, if that doesn't work try this

if (!document.getElementsByClassName) {
    document.getElementsByClassName=function(cn) {
        var allT=document.getElementsByTagName('*'), allCN=[], i=0, a;
        while(a=allT[i++]) {
            a.className==cn ? allCN[allCN.length]=a : null;
        }
        return allCN
    }
}

In some browsers there is a document.getElementsByClassName(class) function. Otherwise, the only option you have is to iterate over all elements in the document by checking each of it against your condition of having the required class name.

Several techniques described and speed tested here: http://ejohn.org/blog/getelementsbyclassname-speed-comparison/

This should work:

function(className)
{
    var matchingItems = [];
    var allElements = document.getElementsByTagName("*");

    for(var i=0; i < allElements.length; i++)
    {
        if(allElements [i].className == className)
        {
            matchingItems.push(allElements[i]);
        }
    }

    return matchingItems;
}

function getElementsByClassName(oElm, strTagName, strClassName){
var arrElements = (strTagName == "*" && oElm.all)? oElm.all :
oElm.getElementsByTagName(strTagName);
var arrReturnElements = new Array();
strClassName = strClassName.replace(/-/g, "\-");
var oRegExp = new RegExp("(^|\s)" + strClassName + "(\s|$)");
var oElement;
for(var i=0; i<arrElements.length; i++){
oElement = arrElements[i];

if(oRegExp.test(oElement.className)){
arrReturnElements.push(oElement);
}

}
return (arrReturnElements)
}