帮我写一个Django和JavaScript的文件上传下载代码，包括上传失败的处理，不使用Django内置的fileForm表单

好的，以下是一个简单的Django和JavaScript文件上传下载代码，能够处理文件上传失败的情况，不使用Django内置的fileForm表单：

在urls.py中添加以下代码：

from django.urls import path
from . import views

urlpatterns = [
    path('upload/', views.upload, name='upload'),
    path('download/<int:id>/', views.download, name='download'),
]

在views.py中添加以下代码：

from django.shortcuts import render, get_object_or_404
from django.http import HttpResponse, JsonResponse
from django.views.decorators.csrf import csrf_exempt
from .models import File

def upload(request):
    if request.method == 'POST':
        file = request.FILES.get('file')
        if not file:
            return JsonResponse({'status': 'error', 'msg': 'Please select a file to upload.'})
        
        name = file.name
        size = file.size
        
        # You can do some additional checks here, such as file type and file size limit.
        # ...
        
        new_file = File(name=name, size=size)
        new_file.save()
        new_file.file = file
        new_file.save()
        return JsonResponse({'status': 'success', 'msg': 'File uploaded successfully.'})
        
    return render(request, 'upload.html')
    
def download(request, id):
    file = get_object_or_404(File, id=id)
    response = HttpResponse(file.file, content_type='application/octet-stream')
    response['Content-Disposition'] = 'attachment; filename="%s"' % file.name
    return response

在models.py中添加以下代码：

from django.db import models

class File(models.Model):
    name = models.CharField(max_length=256)
    size = models.IntegerField()
    file = models.FileField(upload_to='uploads/')

在upload.html中添加以下代码：

<form id="uploadForm" enctype="multipart/form-data" method="post" action="{% url 'upload' %}">
    {% csrf_token %}
    <input type="file" name="file" required>
    <button type="submit">Upload</button>
</form>

在JavaScript中添加以下代码，使用jQuery库简化操作：

$(document).ready(function() {
    $('#uploadForm').submit(function(event) {
        event.preventDefault();
        
        var formData = new FormData(this);
        
        $.ajax({
            url: $(this).attr('action'),
            type: 'POST',
            data: formData,
            success: function(response) {
                alert(response.msg);
            },
            error: function(xhr, status, error) {
                alert('An error occurred during file upload:\n' + error);
            },
            cache: false,
            contentType: false,
            processData: false
        });
    });
});

此代码中，上传的文件会保存在/media/uploads/目录下，你需要确保该目录已经存在并且可写。如果需要修改上传路径，可以在File类中的file字段的upload_to参数中定义。