jquery deferred in .each loop

问题

This should be a simple one. I have a function that is called and I need to wait for all the async operations to complete. what I want is something like this...

self.processSchema(data).done(function(results){ //do stuff});

The processSchema function loops using $.each and calls an async method.

var processSchema = function(data)
{
     var def = new $.Deferred();
     $.each(table, function()
     {
         //calls an async SQLitePlugin method
         db.executeSql(sql, data, function(tx, results){
            def.resolve(results);
         }
     }

     return(def.promise());
}

This does not seem to work, I am new to $.Deferred so any guidance would be helpful

回答1:

You'll need a promise for each iteration

var processSchema = function(data) {
     var promises = [];

     $.each(table, function() {
         var def = new $.Deferred();
         db.executeSql(sql, data, function(tx, results){
            def.resolve(results);
         });
         promises.push(def);
     });

     return $.when.apply(undefined, promises).promise();
}

回答2:

For Functional Programming fiends (like myself), here's a single-expression version of adeneo's answer:

var processSchema = function(data) {
    return $.when.apply($, $.map(table, function() {
        var def = new $.Deferred();
        db.executeSql(sql, data, function(tx, results){
            def.resolve(results);
        });
        return def;
    })).promise();
};

Also I'd like to note that you are iterating over table, but aren't doing anything with each item in the iteration (i.e. the callback in your each has no arguments.) Now, I'm not sure what your goal is, but this doesn't seem right to me :P

来源：https://stackoverflow.com/questions/20688803/jquery-deferred-in-each-loop

标签

javascript

jquery

loops

deferred