Disable/Enable Submit Button until all forms have been filled

Question

I want my form submit button to be disabled/enabled depending on if the form is completely filled.

When the inputs are filled, the disabled button changes to enabled

Answer 1

Just add an else then:

function checkform()
{
    var f = document.forms["theform"].elements;
    var cansubmit = true;

    for (var i = 0; i < f.length; i++) {
        if (f[i].value.length == 0) cansubmit = false;
    }

    if (cansubmit) {
        document.getElementById('submitbutton').disabled = false;
    }
    else {
        document.getElementById('submitbutton').disabled = 'disabled';
    }
}