How to change running site content with JavaScript?

Question

Assume that, there are many checkboxes in any site and they are unchecked. Site works in any server. I have not site code. I want to make checked some of those checkboxes. To find checkboxes by value of <td> Can I do this with JavaScript? How can I run JavaScript code in that site code? My aim is to show checkboxes as "checked".

<tr>
            <td id ="id1" name"name1">value1</td>
            <td><input id="checkid1" name="checkname1" type="checkbox" value="false"></td>
</tr>
<tr>
            <td id ="id2" name"name2">value2</td>
            <td><input id="checkid2" name="checkname2" type="checkbox" value="false"></td>
</tr>
<tr>
            <td id ="id3" name"name3">value3</td>
            <td><input id="checkid3" name="checkname3" type="checkbox" value="false"></td>
</tr>

If it is possible, I want to enter, value1, value2 and JavaScript will make checked related checkboxes.

Answer 1

You can achieve this with JQuery. Check if a checkbox is checked and than set checked true for the desired other checkboxes.

http://jquery-howto.blogspot.be/2008/12/how-to-check-if-checkbox-is-checked.html

To search by value you can do something like this:

$("input:checkbox[value=val]").attr("checked", true);