[javascript] Change value of input and submit form in JavaScript

I'm currently working on a basic form. When you hit the submit button, it should first change the value of a field, and then submit the form as usual. It all looks a bit like this:

<form name="myform" id="myform" action="action.php">
    <input type="hidden" name="myinput" value="0" />
    <input type="text" name="message" value="" />
    <input type="submit" name="submit" onclick="DoSubmit()" />
</form>

And this is how far I've come with the JavaScript code. It changes "myinput"'s value to 1, but it does not submit the form.

function DoSubmit(){
  document.myform.myinput.value = '1';
  document.getElementById("myform").submit();
}

You can use the onchange event:

<form name="myform" id="myform" action="action.php">
    <input type="hidden" name="myinput" value="0" onchange="this.form.submit()"/>
    <input type="text" name="message" value="" />
    <input type="submit" name="submit" onclick="DoSubmit()" />
</form>

document.getElementById("myform").submit();

This won't work as your form tag doesn't have an id.

Change it like this and it should work:

<form name="myform" id="myform" action="action.php">

Here is simple code. You must set an id for your input. Here call it 'myInput':

var myform = document.getElementById('myform');
myform.onsubmit = function(){
    document.getElementById('myInput').value = '1';
    myform.submit();
};

You're trying to access an element based on the name attribute which works for postbacks to the server, but JavaScript responds to the id attribute. Add an id with the same value as name and all should work fine.

<form name="myform" id="myform" action="action.php">
  <input type="hidden" name="myinput" id="myinput" value="0" />
  <input type="text" name="message" id="message" value="" />
  <input type="submit" name="submit" id="submit" onclick="DoSubmit()" />
</form>

function DoSubmit(){
  document.getElementById("myinput").value = '1';
  return true;
}

No. When your input type is submit, you should have an onsubmit event declared in the markup and then do the changes you want. Meaning, have an onsubmit defined in your form tag.

Otherwise change the input type to a button and then define an onclick event for that button.

My problem turned out to be that I was assigning as document.getElementById("myinput").Value = '1';

Notice the capital V in Value? Once I changed it to small case, i.e., value, the data started posting. Odd as it was not giving any JavaScript errors either.

This might help you.

Your HTML

<form id="myform" action="action.php">
<input type="hidden" name="myinput" value="0" />
<input type="text" name="message" value="" />
<input type="submit" name="submit" onclick="save()" />
</form>

Your Script

    <script>
        function save(){
            $('#myinput').val('1');
            $('#form').submit();
        }
    </script>