How to use confirm alert and return an AJAX promise?

Question

I have an existing function that returns an AJAX promise. I want to update this function to display a confirmation alert before running the AJAX call, but other parts of the code use this function and is already expecting a promise.

Here's what my original function looks like:

function doTheDeed() {
  return $.ajax({
    url: '/api/delete/123',
    method: 'POST'
  }).done(function () {
    alert('The deed is done.');
  });
}

doTheDeed().done(function {} { /*Do something else*/ });

Now I want to confirm with the user before running the AJAX call. How do maintain the API agreement of returning a promise, while waiting for the users confirmation or cancel?

function doTheDeed() {
  bootbox.confirm('Are you sure?', function (result) {
    if (result) {
      // Too late to return a promise, promise should've been returned a long time ago
      return $.ajax({
        url: '/api/delete/123',
        method: 'POST'
      }).done(function () {
        alert('The deed is done.');
      });
    } else {
      //return what??
    }
  });
}

doTheDeed().done(function {} { /*Do something else*/ });

Do I need to conditionally return different promises based on the user's response?

Answer 1

You could use jQuery's Deferreds ?

function doTheDeed() {
    var def = $.Deferred();

    bootbox.confirm('Are you sure?', def.resolve);

    return def.promise().then(function(result) {
        return result ? $.post('/api/delete/123') : "no go";
    });
}

doTheDeed().done(function (data) { 
    if (data == 'no go') {
        // user declined
    } else {
        // item deleted
    }
}).fail(function(err) {
    // something failed
});

Answer 2

Building on Adeneo's answer, and adhering to the principle of promisifying at the lowest level, bootbox could be monkeypatched with a reusable promisification of bootbox.confirm() , without having to hack into bootbox itself.

If you do this then it will be appropriate :

• to allow the challenge text and noGo message to be specified by the caller.
• to send the noGo condition down the error path.

if(!bootbox.confirmAsync) {
    bootbox.confirmAsync = function (challenge, noGoMessage) {
        challenge = challenge || 'Are you sure?';
        noGoMessage = noGoMessage || 'User declined';
        return jQuery.Deferred(function (def) {
            bootbox.confirm(challenge, function (confirmed) {
                confirmed ? def.resolve() : def.reject(new Error(noGoMessage));
            });
        }).promise();
    }
}

doTheDeed() would then comprise a totally conventional then chain starting with bootbox.confirmAsync(...) , for example :

function doTheDeed () {
    return bootbox.confirmAsync('Are you sure you want to delete?', 'User declined to delete')
    .then(function (data) {
        return $.post('/api/delete/123');
    })
    .then(null, function (err) {
        // if user declined, then 'User declined to delete' will come back as err.message
        console.log(err.message);
        return err; // jQuery v<3.0
        // throw err; // jQuery v>=3.0
    });
}