Question

<form id="check" action="." method="POST">
    <input id="act" type="hidden" name="action"/>
        <select id="blk">
            <option value="blk">Bulk Actions</option>
            <option value="tes">Active</option>
            <option>Inactive</option>
            <option>Delete</option>
        </select>
     <input type="submit" value="Submit" onclick="document.getElementById('act').value = 'document.getElementById('blk').selectedIndex.value'"/>
</form>

i want get the value by select tag and the value action will be change on input with name action as the value

Answer 1

You’ve mixed two concepts.

• The select element has a value property that reflects the current selection

document.getElementById('blk').value

• The select element has a list of options with values and a selectedIndex property that reflects the position of the current selection. Use it like this:

var sel = document.getElementById('blk');
if (sel.selectedIndex >= 0) // could be -1 as well
    return sel.options[sel.selectedIndex].value

However, what you actually seem to want is

<form id="check" action="." method="POST">
    <select name="action">
         <option value="blk">Bulk Actions</option>
         <option value="tes">Active</option>
         <option>Inactive</option>
         <option>Delete</option>
    </select>
    <input type="submit" value="Submit" />
</form>

You forgot the name of your select control, so no value would be posted. With it, you neither need a hidden input nor a click listener on the button (which should have been a onsubmit listener on the form as well).