How do you set up a local testing server?

Local files versus remote files

Throughout most of the learning area, we tell you to just open your examples directly in a browser — this is done by double clicking the HTML file, or dragging and dropping it into the browser window, or choosing File > Open... and navigating to the HTML file, etc. There are many ways to achieve this.

You know if you are running the example from a local file because the web address will have file:// at the start of it, followed by the path to the file on your local hard drive. In contrast, if you view one of our examples hosted on GitHub (or an example on some other remote server), the web address will have http:// or https:// at the start of it, to show that the file has been received via HTTP.

The problem with testing local files

Some examples won't run if you open them as local files. This can be due to a variety of reasons, the most likely being:

• They feature asynchronous requests. Some browsers (including Chrome) will not run async requests (see Fetching data from the server) if you just run the example from a local file. This is because of security restrictions (for more on web security, read Website security).
• They feature a server-side language. Server-side languages (such as PHP or Python) require a special server to interpret the code and deliver the results.

Running a simple local HTTP server

To get around the problem of async requests, we need to test such examples by running them through a local web server. One of the easiest ways to do this for our purposes is to use Python's SimpleHTTPServer module.

To do this:

1. Install Python. If you are using Linux or Mac OS X, it should be available on your system already. If you are a Windows user, you can get an installer from the Python homepage and follow the instructions to install it:

   • Go to python.org
   • Under the Download section, click the link for Python "3.xxx".
   • At the bottom of the page, choose the Windows x86 executable installer and download it.
   • When it has downloaded, run it.
   • On the first installer page, make sure you check the "Add Python 3.xxx to PATH" checkbox.
   • Click Install, then click Close when the installation has finished.

2. Open your command prompt (Windows)/terminal (OS X/Linux). To check Python is installed, enter the following command:

   python -V

3. This should return a version number. If this is OK, navigate to the directory that your example is inside, using the cd command.

   # include the directory name to enter it, for example
   cd Desktop
   # use two dots to jump up one directory level if you need to
   cd ..

4. Enter the command to start up the server in that directory:

   # On Mac and Linux
   python -m SimpleHTTPServer
   # On Windows
   python -m http.server

5. By default, this will run the contents of the directory on a local web server, on port 8000. You can go to this server by going to the URL localhost:8000 in your web browser. Here you'll see the contents of the directory listed — click the HTML file you want to run.

Running server-side languages locally

Python's SimpleHTTPServer module is useful, but it doesn't know how to run code written in languages such as PHP or Python. To handle that you'll need something more — exactly what you'll need depends on the server-side language you are trying to run. Here are a few examples:

• To run Python server-side code, you'll need to use a Python web framework. You can find out how to use the Django framework by reading Django Web Framework (Python). Flask is also a good (slightly less heavyweight) alternative to Django. To run this you'll need to install Python/PIP, then install Flask using pip3 install flask. At this point you should be able to run the Python Flask examples using for example python3 python-example.py, then navigating to localhost:5000 in your browser.
• To run Node.js (JavaScript) server-side code, you'll need to use raw node or a framework built on top of it. Express is a good choice — see Express Web Framework (Node.js/JavaScript).
• To run PHP server-side code, you'll need a server setup that can interpret PHP. Good options for local PHP testing are MAMP (Mac and Windows) and AMPPS (Mac, Windows, Linux). These are complete packages that create local setups to allow you to run the Apache server, PHP, and MySQL databases.