Changing background color of all elements with the same class

Question

I have a link and a table row that have matching classes. When the link is clicked, I would like to change the background color of the row with the same class. For each case, there will be only one row with the same class.

Here is my current function.

   <script type="text/javascript">

function check(x) {
    elements = document.getElementsByClassName(x);
    for (var i = 0; i < elements.length; i++) {
        elements[i].bgColor="blue";
    }
}
</script>

Here is a part of the table row script:

<tr class="alt1 12">
<td width="50" height="55">
<img src="iPhone/statusicon/12.png" alt="" id="forum_statusicon_12" border="0"></td>
<td>
<div class="forumtitle">
<a class="forumtitle 12" href="forumdisplay.php?f=12" action="async" onclick="check(this.className.split(' ')[1])">News and Current Events</a></div>
</td>
<td width="25">
<div class="forumarrow"><img src="iPhone/chevron.png" alt="" border="0"></div>
</td>
</tr>

The table row has two classes, and I need the second one (the number) to be what is addressed. The current code gives the error "An invalid or illegal string was specified"

Answer 1

You have several errors. You mixed classes with ids and also the class property is actually className

<script type="text/javascript">

function check(x) {
    elements = document.getElementsByClassName(x);
    for (var i = 0; i < elements.length; i++) {
        elements[i].style.backgroundColor="blue";
    }
}

</script>

<a href="#" class="first" onclick="check(this.className)">change first row</a>
<a href="#" class="second" onclick="check(this.className)">change second</a>
<!--        FIX ( id -> class )                FIX ( class -> className ) -->
<table>
<tr class="first">
<td>test1</td>
</tr>


<tr class="second">
<!--FIX ( id -> class ) -->
<td>test2</td>
</tr>
</table>

Check this jsfiddle

Answer 2

You can also do it easily without jQuery with querySelectorAll():

<script type="text/javascript">

function check(selector)
{
    var elements = document.querySelectorAll(selector);
    for (var i = 0; i < elements.length; i++) {
        elements[i].style.backgroundColor = "blue";
    }
}
</script>

<a href="#" class="first" onclick="check('.' + this.className)">change first row</a>
<a href="#" id="second" onclick="check('#' + this.id)">change second</a>

<table>
<tr class="first">
    <td>test1</td>
</tr>


<tr id="second">
    <td>test2</td>
</tr>

Answer 3

jQuery simplifies it:

$(".button").click(function(){
 var class = $(this).attr("data-class");
 var color = $(this).attr("data-color");
 $("."+class).css("background-color",color);
});

.button is the class to apply to the button, add data-class for the class you would like to change the background color of, and data-color is the color you would like to change it to.