On 3/29/14, 5:55 AM, Paolo Amadini wrote:
With bug 988122 landing soon, you'll now find a "Promise" object available by default in the global scope of JavaScript modules.However, this default implementation is still limited, and you're strongly recommended to import Promise.jsm explicitly in new modules: Cu.import("resource://gre/modules/Promise.jsm"); This will give you a number of advantages, among others: - Errors don't risk disappearing silently (bug 966452) - Tests will fail if errors are accidentally uncaught (bug 976205) - You can inspect the current state in the debugger (bug 966471) - You can see registered "then" handlers (bug 966472) - You get better performance on long Promise chains Promise.jsm and Promise are still interoperable from the functional point of view, the difference is in the above non-functional characteristics. Promise.jsm also has better performance due to the fact that it avoids the JavaScript / C++ / JavaScript turnaround time on chain resolution, with an optimized resolution loop handling, but I don't think this performance part should prevent us from migrating to C++ Promises when the other limitations are addressed.
If Promise.jsm is obviously superior, why don't we expose that version to chrome-privileged global scopes by default? One less footgun.
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