jsFiddle

JsFiddle is a service to easily share and edit snippets of HTML and Javascript code. As most of the early games you will be making are small in size, this service will be ideal for this. You can run your code in the same screen and this way you will be able to immediately see the changes you make reflected on your screen.

This fiddle is already configured to run the Phaser Game Engine so you can immediately start to write your code in the Javascript window.

Github

When you are making bigger games jsFiddle might start to become harder to work with. To solve this I made a quickstart repository on Github. You can fork (See here for more information on how Github works) this and edit it with your favorite editor (See here for more information on how to set up an editor). The repository is set up to immediately build your game and host it on Github Pages.