Firefox引导扩展，在顶级导入时的竞争条件？

Question

I'm trying to get myself familiar with Firefox bootstrapped add-ons. Consider following example:

// bootstrap.js

'use strict'

function alert(message) {
    var prompts = Components.classes["@mozilla.org/embedcomp/prompt-service;1"].getService(Components.interfaces.nsIPromptService);
    prompts.alert(null, "from my extension", message);
}

try {
    Components.utils.import('chrome://my-ext/content/foo.jsm');
    alert('ok');
} catch(e) {
    alert(e);
}

And chrome://my-ext/content/foo.jsm being just this.EXPORTED_SYMBOLS = []; .

The issue with an above code sample is that it does not work each time. It may fail with NS_ERROR_FILE_NOT_FOUND instead of importing, or may say OK — despite the fact later, when browser starts, I can access foo.jsm through location bar.

Does this mean I should not import anything in the top level, because chrome registration might not be done yet, or problem is in something else?

Answer 1

NB The following is my experience and may not be definite

bootstrap.js of bootstrapped addon run when browser starts and BEFORE any WINDOW or DOM is created.

bootstrap.js also has a order and specific format for execution.

Is above example the way your bootstrap.js is?

You can import Firefox modules anywhere (although I would always do so on top).

It is best to execute your Components.utils.import('chrome://my-ext/content/foo.jsm'); within function startup(data, reason) { ... }

Additional Notes/Suggestions:

Generally, I would assign var prompts outside a function so that it is not reassigned every time a function is run. I would also use Services.jsm for ease of use (but it make no difference at all) eg:

Components.utils.import('resource://gre/modules/Services.jsm');

// then anywhere in the code
Services.prompt.alert(null, title, text);

Habitually, I do all Firefox built-in modules imports Components.utils.import() on top of the JS/JSM
Firefox built-in modules (not addon's modules) are cached by Firefox and there is no need to Components.utils.unload() them.