Development/Tutorials/Plasma4/JavaScript/CheatSheet

Basics

Everything but the metadata.desktop file goes in a directory named contents
X-Plasma-MainScript in the metadata.desktop file should point to the main script, relative to the contents directory
X-Plasma-DefaultSize in the metadata.desktop file specifies the default widget size in width,height format (eg: 200,100)
The plasmoid variable contains all the main plasmoid functionality and represents the main plasmoid widget, and corresponds to the Applet class in C++
plasmoidviewer is an immensely useful tool
To connect to a signal use object.signalName.connect(function() {});
Enumeration values can be used like

if (plasmoid.formFactor() == Vertical) {

   layout.setOrientation(QtVertical);

} else {

   layout.setOrientation(QtHorizontal);

}

The Name and Comment fields in the metadata.desktop file can be translated like Name[nl]=Hallo JavaScript
plasmoid.i18n() takes a string (in English) as the first argument, and substitutes in the following arguments to replace %1, %2, %3 etc. Eg: plasmoid.i18n("The file is called %1", fileName);
plasmoid.i18nc() works just the same, but has an extra argument at the start that provides some context for translators. Eg: plasmoid.i18nc("Player name - score", "%1 - %2", playerName, score);
plasmoid.i18np() is for cases where plural forms might be important. Eg: plasmoid.i18np("One image in album %2", "%1 images in album %2", imageCount, albumName);
plasmoid.i18ncp() is a combination of the previous two. Eg: plasmoid.i18ncp("Personal file", "One file", "%1 files", numFiles);

Add a dataUpdate method to plasmoid to receive updates: plasmoid.dataUpdate = function(name, data) { /* ... */ } - data contains an object mapping keys to values
plasmoid.dataEngine("engine name").connectSource("source name", plasmoid, 500); updates every half second
plasmoid.dataEngine("engine name").connectSource("source name", plasmoid); updates when new data is available
plasmaengineexplorer is your friend

DO NOT use plasmoid.dataEngine("engine name").serviceForSource("source name") - you will get a dummy service back (in 4.2 at least).
Instead, use plasmoid.service("engine name", "source name")