Promise after jQuery each

Question

I'm trying to invoke a function after my $.each() finishes using a promise. However, when I try the following code I get Uncaught TypeError: $.each(...).promise is not a function.

$.each(snapshot.val(), function(chat, i){
    firebase.database().ref('chats/'+chat+'/msgs').once('value', function(snap){
        if (Object.keys(snap.val())[0] != i){
              notification = true;
        } 
    });
}).promise().done( function(){ alert("All was done"); } );

I'm relatively new to promises, can anyone let me know how I can fix this please?

Answer 1

so if that function passed to once is your callback, the following should help you out.

var promises = [];

$.each(snapshot.val(), function(chat, i){
    var dfd = $.Deferred();
    firebase.database().ref('chats/'+chat+'/msgs').once('value', function(snap){
        if (Object.keys(snap.val())[0] != i){
            notification = true;
        }
        dfd.resolve();
    });
    promises.push(dfd);
})

$.when.apply($, promises).done(function () {
    alert("All was done");
});