使用$ q Promise，将参数传递给下一个函数

Question

For promises, is there an accepted method to pass more than one parameter to the next function in a promise chain?

Some background:

I have a project in which we are using promises to handle asynchronous calls to a database. I have a function in a library we are using that's roughly of the form:

executeSql(statement, options, successCallback, failCallback)

Since this is in a long string of promises, I need to make it also into a promise so I can .then it.

I tried the following:

$q(function(resolve, reject) {
    executeSql(statement, options, resolve, reject);
}).then(function(tx, results) {
    alert(tx);
    alert(results);
}

The first parameter comes through fine, but the second does not. If I do this:

executeSql(statement, options, function(tx, results) {
    alert(tx);
    alert(results);
}, null);

everything works as expected.

It seems like a promise only sends a single parameter to the next .then function. Unfortunately, since the first one is the one I don't care about and only one gets sent along, I have no way to access the results.

I have a workaround for this specific issue, but my general question remains.

For reference, the workaround is:

$q(function(resolve, reject) {
    executeSql(statement, options, function(tx, results) {
        resolve(results);
    }, reject);
 });

But that only works because I only care about passing on the results in this particular case.

Answer 1

According to the AngularJS $q API , you can only pass a single parameter to the resolve function. So to pass multiple variables you'd have to wrap them in an object. Ie you could call:

resolve({'tx':tx, 'results':results})

and your then function would look something like:

.then(function(wrapperObj) {
  alert(wrapperObj.tx);
  alert(wrapperObj.results);
})