You have to do the processing on the results from the db query on a callback only. Just like. function getColour(username, roomCount, callback) { connection.query(‘SELECT hexcode FROM colours WHERE precedence = ?’, [roomCount], function(err, result) { if (err) callback(err,null); else callback(null,result[0].hexcode); }); } //call Fn for db query with callback getColour(“yourname”,4, function(err,data){ if (err) { … Read more
Very simply, a callback needn’t be asynchronous. http://docs.apigee.com/api-baas/asynchronous-vs-synchronous-calls Synchronous: If an API call is synchronous, it means that code execution will block (or wait) for the API call to return before continuing. This means that until a response is returned by the API, your application will not execute any further, which could be perceived by … Read more
So if I want to pass a list to my callback function through WinApi I use GCHandle // object to IntPtr (before calling WinApi): List<string> list1 = new List<string>(); GCHandle handle1 = GCHandle.Alloc(list1); IntPtr parameter = (IntPtr) handle1; // call WinAPi and pass the parameter here // then free the handle when not needed: handle1.Free(); … Read more
I use anonymous functions for three reasons: If no name is needed because the function is only ever called in one place, then why add a name to whatever namespace you’re in. Anonymous functions are declared inline and inline functions have advantages in that they can access variables in the parent scopes. Yes, you can … Read more
Example using JS Bind Doc: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/bind Tip, the bound parameters occur before the call-time parameters. my_hello = ‘Hello!’ my_world = { ‘antartica’: ‘cold’, } anonymous_callback = function (injected1, injected2, param1, param2) { param1 = param1 ? param1 : ‘One’; param2 = param2 ? param2 : ‘Two’; console.log(‘param1: (‘ + typeof(param1) + ‘) ‘ + param1) … Read more
Yes you are in callback hell. The solution assuming you don’t want to use async (which I doubt you can justify other than prejudice) consists of: 1) Make more top-level functions. Each function should perform either 1 or 2 IO operations as a rule of thumb. 2) Call those functions, making your code follow a … Read more
You’ve just hit a big limitation in JavaScript. Once your code enters the asynchronous world, there is no way to get back to a classic procedural execution flow. In your example, the solution would be to make a loop waiting for the response to be filled. The problem is that JavaScript does not provide any … Read more
around_* callbacks are invoked before the action, then when you want to invoke the action itself, you yield to it, then continue execution. That’s why it’s called around The order goes like this: before, around, after. So, a typical around_save would look like this: def around_save #do something… yield #saves #do something else… end
The notion of “returning” values from callbacks doesn’t make sense in the context of an event driven program. Callbacks are called as the result of an event, so there’s nowhere to return a value to. As a general rule of thumb, your callbacks should always call a function, rather than using functools.partial or lambda. Those … Read more
You can call it as follows, var callBack = function(param1, param2) { … } window.setTimeout( function(){callBack(‘foo’,’bar’);}, 1000 );