JavaScript

What is Dependency Injection?

I've answered this a couple times so I'm writing it down :)

DI is a way to separate services from the code that uses those services.

DI makes testing easier. It also allows the services to be replaced with alternatives - but this is less important than the testing.

DI is used in Angular, Zend Framework 2, Symfony and more frameworks.

DI is implemented as an array or dictionary of services with generic names. Services are created during startup, and registered.

CORS, Angular JS, and Parse.com, together, didn't let me login twice.

Things were going well with a re-architecting and re-factoring of a service to use Angular's awesome $request, and Django REST Frameworks' awesome ModelViewSet generics. As usual, when things are chugging along, you come across a weird bug that just sucks you in for a while. The bug I hit today involved CORS, AngularJS, and Parse (we're using Parse for part of our backend).

The symptom was that, if I logged in once, then logged out, I could not log in again. I could reach the server, but it wouldn't let me do the exact same thing I'd done just 30 seconds before.

Not Hating on HATEOAS

There's been some loving and some hating on HATEOAS (which I don't know how to pronounce), but I'm starting to get it. See: REST Cookbook, Timeless, and PayPal's API.

The core idea is, in addition to the data, you send over some information about the possible URLs you can use as a next step.

Promises, promises (in Javascript)

This is a short explanation of what promises are, and how they work.

You're probably familiar with callbacks, where you pass a function as an argument to another function, like this:

   f( function b() {...});

When f does something, usually taking some time, it runs b.

Promises are just callbacks with a little more structure.

There's a library called Q that's influencing frameworks like Angular. Q's most visible quality is that it uses a differen syntax:

 

Demo of rotating an element to make a "dial" or "knob" ui element

Here's a little bit of code that shows how to create a "dial" knob that you can control with the mouse. It's entirely in HTML, CSS and Javascript.

It's not hard, but there are a lot of little details to make it look reasonable and not completely goofy. I think it moves a little weird - and it should respond to both x and y axes, but doesn't.

The sum of two sines, with an offset.

Cast any Javascript Value to a Boolean with Double Exclamation

It's a way to cast any variable to a boolean.

var x = true;

!!x === true; // this is a fact

Sometimes, we do a check on an object:

if (window.foo) {
  ...
}

However, if we assign a variable like this:

var isFoo = window.foo;

isFoo will now contain a reference to window.foo. 
If you want isFoo to contain the truthyness of 
window.foo, you do this:

var isFoo = !!window.foo;

Nesting Angular Directives

I've been learning how to write directives, and it's really tough to grok how to do it. This blog post's been rewritten three times so I don't come off as totally ignorant about the "right way" or "the Angular way" to do things.

What I'm trying to do it implement a menu display with lightweight, role-based control over what is displayed.

My first iteration was done entirely with controllers, HTML, and jQuery and plain Javascript. That was clearly not the Angular way, so I revised it a little bit - CSS animations, and let's use directives.

Angular Service and Factory

I was reading the docs, and read things that seemed to contradict what I thought. I thought that Services were singletons, and Factories were instantiating new instances. It turns out that's not quite right. It's explained well here.

Base32 Encoding and Decoding in Javascript

This is a simple implementation of base 32 encoding and decoding that conforms to RFC 4648.

Battle of the Naming Conventions (how to avoid them in Django REST Framework)

Python and Django like snake_case.

AngularJS feels like Java, and likes camelCase.

HTML likes dashed-words.

MySQL docs like snake_case, but I see more PascalCase used in databases. It's case-sensitive, too.

Parse.com uses PascalCase for tables/classes, and camelCase for columns/properties/fields. That's like Java OOP.

Django likes to append _id to your primary keys.

So... the problems start to happen when one piece of named data is passed from one layer of the system to another. It's just a good policy to use the same names at all layers, if possible.

Benchmarking String Function to camelCase

I needed a function to turn snake_case to camelCase. The reason why? Angular and Javascript are better with camelCase, and Python and Django prefer snake_case. I tried working with both in the Django side, and it wasn't pretty. Even worse, I lost track of when I switched from one to the other, if I switched at all. So, I'm going to try renaming the keys as they are handed off from Django Rest Framework to the Javascript.

AngularJS Directive: Stretchdown - stretches an element to the bottom of the window.

I've made may first directive! OK, not that special, but to me it is. This is one of the more difficult features I've come across in Angular, and I still don't really "get it".

[I didn't "get it" because I used directives as a mixin to implement a UI feature. Directives are really supposed to be for encapsulating HTML into small templates.]

I'm not even going to do a code walkthrough, because I can't really explain it well. The easy part is calculating the height the element should be. The tricky part is implementation.

Button to Scroll to Top of the Page

Mobile websites all seem to have this button, which appears when you've scrolled down a bit. The button scrolls you back to the top of the page, where most of the menus reside.

Create JavaScript Functions from Strings: Code Generation

One of the less-used features is the Function() object, which can turn a string of Javascript code into a function. This is an example of how it can be useful.

I recently hit an annoyance with the Android browser. Around version 3 and 4 of Android, the browser stopped supporting the JS history.pushState() and history.replaceState() methods, basically killing my LA IMC JS app.

Just to verify, I wrote the following to test the existence of those objects:

<script>
if (history) {
  document.write("history supported<br />");
}
if (history.back) {

Bookmarklet to Mass-Unfollow Twitter Users

I almost wrote a page for this, but it turns out a bookmarklet is good enough:

javascript:$('.js-follow-btn').click();undefined;
Syndicate content