Restartless Add-ons – Default Preferences

I saw a neat technique in Bug 564675 for creating default preferences in bootstrapped add-ons. Edward Lee posted a link to some code he uses for a bootstrapped add-on. Essentailly, the default preference branch is writable, but not permanent. This is a good thing for bootstrapped add-ons. The add-on should write it’s default preferences every time it loads and the preferences disappear when the session ends. The code looks like:

const PREF_BRANCH = "extensions.myaddon.";
const PREFS = {
  someIntPref: 1,
  someStringPref: "some text value"
};

function setDefaultPrefs() {
  let branch = Services.prefs.getDefaultBranch(PREF_BRANCH);
  for (let [key, val] in Iterator(PREFS)) {
    switch (typeof val) {
      case "boolean":
        branch.setBoolPref(key, val);
        break;
      case "number":
        branch.setIntPref(key, val);
        break;
      case "string":
        branch.setCharPref(key, val);
        break;
    }
  }
}

function startup(aData, aReason) {
  // Always set the default prefs as they disappear on restart
  setDefaultPrefs();
  ...
}

I haven’t tested to see if there is a clean way to remove these preferences when a bootstrapped add-on is disabled or uninstalled. The default preferences will likely still hang around until a shutdown occurs.

We’re starting to amass a sizable collection of code snippets for bootstrapped add-ons. I think a new section in the MDC Code Snippets area might be needed.