input.select() does not work on iOS

The recommended method to give a text field focus and select its contents is the following:

document.getElementById('myInput').select();

However, this does not work in iOS. The correct way to do it is to use setSelectionRange on an already focused input.

var input = document.getElementById('myInput');
input.focus();
input.setSelectionRange(0,99999);

setSelectionRange will not work on iOS if the element doesn’t have focus. Also be advised that anything revolving around giving text inputs focus is highly unreliable on mobile Safari.

Using CSS3 transforms and calc() in Internet Explorer

Although CSS calc sizes are supported in Internet Explorer 10 and above, they do not work when used in transform attributes. For instance, transform: translate(0, calc(100% - 10px)); does not work in Internet Explorer.

To work around this, you can chain transforms. For instance, the following statements are equivalent:

transform: translate(0, calc(100% - 10px)); //Does not work in IE
transform: translate(0, 100%) translate(0, -10px); //Works in IE

It’s that simple!

How to fix slow file read/write in Node.js

This morning, I had trouble with one of my grunt tasks taking several minutes to finish instead of 3-4 seconds. After a bit of troubleshooting, I isolated the bottleneck to a bunch of seemingly harmless file reads.

Guess who was the culprit? The company-supplied McAfee. Turning off on-access scan immediately fixed the issue and dropped the build time from 3 minutes to 5 seconds.

Django DeleteView with AJAX

The default Django generic DeleteView is not perfectly adapted for AJAX requests. A much simpler AjaxDeleteView can easily be implemented using the same mixins as Django’s generic class-based views:

class AjaxDeleteView(SingleObjectMixin, View):
    """
    Works like DeleteView, but without confirmation screens or a success_url.
    """
    def post(self, *args, **kwargs):
        self.object = self.get_object()
        self.object.delete()
        return HttpResponse(status=204)

This views performs CSRF validation just like the default DeleteView, except it won’t show any confirmation screens and has no need for the success_url attribute.

Return a user’s own objects with Django’s class-based views

There is a very simple way to only return the connected user’s own objects with Django’s generic class-based views.

When you extend get_queryset() on any view that implements SingleObjectMixin or MultipleObjectMixin (almost all of them), you can filter the default QuerySet to match your needs. It becomes fairly easy to create a mixin that filters any queryset to return objects created by the current user.

This is the mixin we will be using:

class OwnObjectsMixin():
    """
    Only returns objects that belongs to the current user. Assumes the object
    has a 'user' foreignkey to a User.
    """
    def get_queryset(self):
        user = self.request.user
        return super(OwnObjectsMixin, self).get_queryset().filter(user=user)

Let’s say you have a Bookmark model that has a foreign key called user that points to the standard User model. UserList view would look like this:

class UserList(OwnObjectsMixin, ListView):
    model = User

class UserDetails(OwnObjectsMixin, DetailView):
    model = User

You can use that mixin with CreateView, DeleteView and UpdateView too, making your views simple and maintainable.

Pagination with Django’s generic ListView

Did you know the Django ListView supports pagination out of the box? All you need to do is specify the number of items per page with the paginate_by attribute:

class ArticleList(ListView):
    model = Article
    paginate_by = 10

The queryset available in object_list will be paginated, so you will only get 10 results. page_obj and paginator will be added to the context so you can have pagination buttons and know which page you are on.

The documentation for this is buried under MultipleObjectMixin’s documentation.