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How to Create a Javascript Program

From AstroEd

Revision as of 18:03, 2 February 2017 by WikiSysop (talk | contribs) (A guide to creating and using javascript as a desktop tool running within a browser, brought to you by python.)

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The browser on your desktop is a computing engine with a well-designed user interface. Behind the interactive environment, it can read local HTML files and execute programs written in javascript. This page is a step-by-step guide to working in that enviroment, with examples and links to get you started with using it as a research tool.


Begin with Python

In order to get started you will need a local web server. Since most likely you will not have one running that is easily accessible, a simple solution is to use python to provide one for you. Python has a built-in module that will run a server and that can be started with one line of python code.

First, identify the directory or folder on your computer under which all of the javascript you want to access is stored. Then, at the top level of that directory, run this program

python -m CGIHTTPServer 8000 1>/dev/null 2>/dev/null &

By using port 8000 the server is distinct from the one on port 80 used for web applications. The site would appear by putting

http://localhost:8000

in a Google Chrome or Mozilla Firefox browser window running on the same user account on the same machine. Note the redirects for stdio and stderr to /dev/null keeps output from appearing in the console. The server may be killed by identifying its process ID in Linux with the command

ps -e | grep python

followed by

kill -s 9  pid

where "pid" is the ID number found in the first line. Alternatively, if it is the only python process running you may kill it with

killall python

Any file in the directory tree below the starting directory is now accessible in the browser, and html files will be parsed to run the included javascript. If here is a cgi-bin directory at the top level, the server will see it and use it. One use of this low level server is to create a virtual instrument that is accessible from the web, but not exposed to it directly. A remote web server on the same network that can access port 8000 on the instrument machine can run code and get response from the instrument by calling cgi-bin operations.

For programmers, however, this utility allows development and debugging of web software without the need for a large server.