> Feature detection needs to be possible without actually calling the
> function--without actually opening a prompt. For example, if you're to run
> the above prompt from a timeout, you need to know that *before* you call
> prompt(), since you don't want a timeout if the async API is supported.
You'd only need to use window.setTimeout() if window.prompt() ignored your
callback argument and didn't return it:
> function promptWrapper(message, default, callback) {
> var result = window.prompt(message, default, callback);
> if (callback && (typeof callback === "function")) {
> if (result !== callback) {
> /*** INSTEAD OF: callback(result); ***/
> window.setTimeout(callback, 1, result);
> }
> return callback;
> }
> return result;
> }
However, as you pointed out, this "feature detection" only occurs after
window.prompt() is invoked. A better way might be to test the
window.prompt.length property (if 3 or more then non-blocking mode is
supported).
> The pattern in new APIs like IDB and FileAPI is to have separate sync and
> async interfaces, not overloaded behavior, eg:
>
> promptAsync(message, default, callback);
>
> Better off just leaving this crusty old API in the legacy bin, though.
Agreed.
