There are a few good code editors for the iPad like Textastic and Koder. These are heavy-weights with a ton of features. But if you look at these, they're just code editors. More like a smart notepad that can highlight syntax.
The Kodiak iPad app looks light-weight and simplistic despite hiding some real power beneath the layers. The PHP app comes prepacked with extensions for MySQL, curl etc. The developers aimed to put everything you'll need to test PHP code here. There are quite a bunch of examples too so you can get started easily.
The Kodiak app comes with a neat file manager so you can create, edit and move around files easily. In the case of JS, you get libraries bundled with the app so frameworks like jQuery, Bootstrap, AngularJS are all available instantly.
There are many other interesting things that Kodiak iPad app brings. These include:
- A special navigation key that makes it easy to move about on a file to edit it
- Syntax highlighting, obviously
- Tabbed editor so you can have multiple files open at the same time
- A clear and simple file manager
Each of the app (PHP and JS) is $9.99. It's totally worth it if you often find yourself firing up the computer to test programs in JS and PHP.