How to Get Element By Class in JavaScript?

I want to replace the contents within a html element so I'm using the following function for that:

function ReplaceContentInContainer(id,content) {
   var container = document.getElementById(id);
   container.innerHTML = content;
}

ReplaceContentInContainer('box','This is the replacement text');

<div id='box'></div>

The above works great but the problem is I have more than one html element on a page that I want to replace the contents of. So I can't use ids but classes instead. I have been told that javascript does not support any type of inbuilt get element by class function. So how can the above code be revised to make it work with classes instead of ids?

P.S. I don't want to use jQuery for this.

This code should work in all browsers.

function replaceContentInContainer(matchClass, content) {
    var elems = document.getElementsByTagName('*'), i;
    for (i in elems) {
        if((' ' + elems[i].className + ' ').indexOf(' ' + matchClass + ' ')
                > -1) {
            elems[i].innerHTML = content;
        }
    }
}

The way it works is by looping through all of the elements in the document, and searching their class list for matchClass. If a match is found, the contents is replaced.

jsFiddle Example, using Vanilla JS (i.e. no framework)

Of course, all modern browsers now support the following simpler way:

var elements = document.getElementsByClassName('someClass');

but be warned it doesn't work with IE8 or before. See http://caniuse.com/getelementsbyclassname

Also, not all browsers will return a pure NodeList like they're supposed to.

You're probably still better off using your favorite cross-browser library.

document.querySelectorAll(".your_class_name_here");

That will work in "modern" browsers that implement that method (IE8+).

function ReplaceContentInContainer(selector, content) {
  var nodeList = document.querySelectorAll(selector);
  for (var i = 0, length = nodeList.length; i < length; i++) {
     nodeList[i].innerHTML = content;
  }
}

ReplaceContentInContainer(".theclass", "HELLO WORLD");

If you want to provide support for older browsers, you could load a stand-alone selector engine like Sizzle (4KB mini+gzip) or Peppy (10K mini) and fall back to it if the native querySelector method is not found.

Is it overkill to load a selector engine just so you can get elements with a certain class? Probably. However, the scripts aren't all that big and you will may find the selector engine useful in many other places in your script.

How to Get Element By Class in JavaScript?

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