Django: How to detect the focus out in django template and call a function on it

Question

I am working on a project. Need help in template focus out events on Django.

model.py

class Route(models.Model):
route_no = models.SmallIntegerField(default=0)
xname = models.CharField(max_length=40)

class Booth(models.Model):
booth_no = models.SmallIntegerField(default=0)
route_no = models.ForeignKey(Route,
                             on_delete=models.CASCADE,
                             db_column='route_no')

View.py

class BoothCreateListView(CreateView, ListView):
model = models.Booth
form_class = booth.BoothForm
template_name = 'booth/booth_create_list.html'
context_object_name = 'booth_list'

def get_context_data(self, **kwargs):
    context = super().get_context_data(**kwargs)
    js_data = list(models.Route.objects.all().values_list('route_no', 'xname'))
    context['js_data'] = json.dumps(list(js_data), cls=DjangoJSONEncoder)
    return context

template/booth_create_list.html

 <div class="col-sm-12 col-md-5">
            <form method="post">
                {% csrf_token %}
                <table class="table table-borderless">
                    {{ form.as_table }}
                </table>
                <input class="btn btn-success" type="submit" value="Save">
            </form>
{{ form.route.value }}
</div>
<div id='route_no'></div>
<script>
    var route_no = document.getElementById('route_no')
    var myfunction = function (){
        console.log('changing');
        route.innerHTML = '{{ check_route_no form.route.value }}'
    }
</script>

form/booth.py

class BoothForm(ModelForm):
class Meta:
    fields = [
        'route_no', 'booth_no',
    ]
    model = models.Booth
    widgets = {
        'route_no': forms.TextInput(),
    }
    labels = {
        'route_no': 'Route No.',
        'booth_no': 'Booth No',
    }

def __init__(self, *args, **kwargs):
    super().__init__(*args, **kwargs)
    self.fields['route_no'].widget.attrs.update(
        {'onfocusout':'myfunction()'}
    )
    for name, field in self.fields.items():
        field.widget.attrs.update(
            {'class': 'form-control form-control-user'}
        )

templatetags/booth_template_tags.py

from booth import models
register = template.Library()

@register.simple_tag
def check_route_no(route_no):
    print(route_no)
    route = models.Route.objects.filter(route_no=route_no)
    if route.count() == 1:
        return route.xname
    else:
        return "not present"

I want to check the route as user types it in the form for the booth. If route_no is present then show the route xname else not present.

My value passed to the template tag is always none. I am not able to pass the textbox value to the template tag to search in DB. Please help to check runtime if the route no is there in DB as the user type.