formcheck.js

function setupValidation(field, timeout) {
  var input = $('#id_'+field);
  var input_tr = $('#id_tr_'+field);
  check = function () {
    var t = this;
    if (this.value != this.lastValue) {
      if (this.timer) clearTimeout(this.timer);
      input_tr.removeClass('error');
      $('#id_tr_errors_'+field).remove();
      this.timer = setTimeout(function () {
        $.getJSON(
          'check?'+field+'='+t.value+'&r='+Math.random(),
          function (data) {
            datr = data;
            if (data.ok) {
            } else {
              html = '<tr id="id_tr_errors_'+field+'"><th colspan=2><ul class="errorlist">';
              for (var i=0; i<data.errors[field].length; i++){
                html += '<li>' + data.errors[field][i] + '</li>';
              }
              html += '</ul></tr>';
              input_tr.after(html);
              input_tr.addClass('error');
            }
          }
        );
      }, timeout);
    }
    this.lastValue = this.value;
  }
  input.keyup(check);
  input.blur(check);
}
var datr;

/* Example: 
$(document).ready(function () {
  $('#id_username').focus();
  setupValidation('username', 500);
  setupValidation('email', 1000);
});
/*

formcheck.py

"""
AJAX server side form validation for django.
"""

from django.http import HttpResponse, Http404
from django.utils.encoding import force_unicode
from jsonutil import JsonResponse

def formcheck(request, form_class=None):
    """
    This view responds with JSON telling you what form errors
    exist in your form before you submit it. Be sure to pass
    it the form class that you want to use, e.g.:

        urlpatterns += patterns('',
            (r'^myformcheck/$', formcheck, {'form': MyForm}),
        )

    You can use either GET or POST.
    """

    form = form_class(request.REQUEST)
    form.is_valid()

    # Build a dictionary of the errors found in fields that 
    # were mentioned in the request.
    # Note that we have to force unicode here to get the JSON
    # serializer not to choke.
    errordict = dict(
        (
            force_unicode(field.name),
            [force_unicode(e) for e in field.errors]
        )
        for field in form
        if request.GET.get(field.name) and field.errors
    )

    return JsonResponse({
        'ok': not errordict,
        'errors': errordict
    })