Using JavaScript to modify HTML pages

This repo shows methods to modify HTML pages dynamically using JavaScript. As an example, the JS for the GNU Radio Conference (GRCon) is explained. See GRCon22.

Installation

Note: These instructions are written for a Linux OS. Similar commands work for Mac and Windows.

1. Open a terminal window.
2. Change to the home directory.

cd ~/  

3. If you don't have 'git', enter

sudo apt install git  

4. Clone the repository:

git clone https://github.com/duggabe/js-html.git

Local Testing

• Open your file manager and go to the `~/js-html folder.

• Open Test3.html in your browser to see the footer format.

• Open Test4.html in your browser to see the Sponsor page format.

• Open Test5.html in your browser to see the Keynote Speakers page format.

References

• HTML JavaScript
• JavaScript Tutorial
• JavaScript HTML DOM

How it works

The JavaScript for the GRCon Indico website is in file sponsors.js. It performs two main functions: (a) generate the footer for every GRCon webpage, and (b) generate the Sponsors page. The interface to the Indico software is done using a JavaScript inserted in the basic page template. That script links to the external script located in https://www.gnuradio.org/indico/sponsors.js.

To make sure that the DOM is completely loaded before the script executes, two lines were added to wait on the 'load' event:

document.body.onload = function() {myFunction()};  
function myFunction() {  

where 'myFunction()' wraps the rest of the script.

Since the same script must support multiple events, determination of individual Sponsor pages is performed in the code. Those Sponsor pages are:

GRCon21 - https://events.gnuradio.org/event/8/page/5-sponsors  
GRCon22 - https://events.gnuradio.org/event/18/page/60-our-sponsors  
GRCon23 - https://events.gnuradio.org/event/21/page/94-our-sponsors  
GRCon24 - https://events.gnuradio.org/event/24/page/143-our-sponsors  

Generate footer

For pages other than the Sponsors page, the existing footer is totally replaced. In the Indico-generated page there is a DIV with a class of "footer " which marks the beginning of the page footer. Since sa = document.getElementsByClassName("footer "); returns an array, sa[0] is the one (only) we need. We start by writing the footer title "Our Sponsors". Next we build a <table> using the tbl = document.createElement("TABLE"); method. In order to apply a class to the table, we use tbl.setAttribute("class", "u_table");. The classes are defined in GRCon22.css. The DCS.css file is only for local testing.

The header row is derived from data in the myObj object. If there is more than one entry which has the same level of sponsorship, the table header for that level is set to span multiple columns. As each entity is built, it is attached to the parent entity.

The data row also is derived from myObj. For each entry, a <td> item is created with a clickable icon linking to the sponsors web site.

Generate Sponsors page

For the Sponsors page, the existing paragraphs are preserved, since they can be edited by the event administator. Below that, sponsors.js creates a vertical listing of sponsor levels, with each entry displaying a clickable icon linking to the sponsors web site on the left portion of the screen, and a short synopsis of what the company does on the right side.

Generate Keynote Speakers page

For GRCon23, code is added to generate the Keynote Speakers page which includes not only the Keynote speakers but also those labeled as Invited Speakers. For each speaker, sponsors.js creates a vertical listing with each entry displaying a clickable photo linking to the speaker's web site on the left portion of the screen, and a short bio on the right side.

Footer last two lines

The original last line of the Indico page has the Indico icon, version number, a "Help" link, and a "Contact" link. The sponsors.js script makes two lines out of this. The first is a revised help / contact portion which is centered on the page. The second line has the Indico icon and version number on the left.