I am going to try to keep this dead simple. A “callback” is any function that is called by another function which takes the first function as a parameter. A lot of the time, a “callback” is a function that is called when something happens. That something can be called an “event” in programmer-speak. Imagine … Read more
Note: Most of the answers cover function pointers which is one possibility to achieve “callback” logic in C++, but as of today not the most favourable one I think. What are callbacks(?) and why to use them(!) A callback is a callable (see further down) accepted by a class or function, used to customize the … Read more
Changing Values: array_map cannot change the values inside input array(s) while array_walk can; in particular, array_map never changes its arguments. Array Keys Access: array_map cannot operate with the array keys, array_walk can. Return Value: array_map returns a new array, array_walk only returns true. Hence, if you don’t want to create an array as a result … Read more
Promises are not callbacks. A promise represents the future result of an asynchronous operation. Of course, writing them the way you do, you get little benefit. But if you write them the way they are meant to be used, you can write asynchronous code in a way that resembles synchronous code and is much more … Read more
This is impossible as you cannot return from an asynchronous call inside a synchronous method. In this case you need to pass a callback to foo that will receive the return value function foo(address, fn){ geocoder.geocode( { ‘address’: address}, function(results, status) { fn(results[0].geometry.location); }); } foo(“address”, function(location){ alert(location); // this is where you get the … Read more
An Objective-C delegate is an object that has been assigned to the delegate property another object. To create one, you define a class that implements the delegate methods you’re interested in, and mark that class as implementing the delegate protocol. For example, suppose you have a UIWebView. If you’d like to implement its delegate’s webViewDidStartLoad: … Read more
Developers are often confused by what a callback is because of the name of the damned thing. A callback function is a function which is: accessible by another function, and is invoked after the first function if that first function completes A nice way of imagining how a callback function works is that it is … Read more
Promises have state, they start as pending and can settle to: fulfilled meaning that the computation completed successfully. rejected meaning that the computation failed. Promise returning functions should never throw, they should return rejections instead. Throwing from a promise returning function will force you to use both a } catch { and a .catch. People … Read more
setTimeout(function() { postinsql(topicId); }, 4000) You need to feed an anonymous function as a parameter instead of a string, the latter method shouldn’t even work per the ECMAScript specification but browsers are just lenient. This is the proper solution, don’t ever rely on passing a string as a ‘function’ when using setTimeout() or setInterval(), it’s … Read more
What you should know about this this (aka “the context”) is a special keyword inside each function and its value only depends on how the function was called, not how/when/where it was defined. It is not affected by lexical scopes like other variables (except for arrow functions, see below). Here are some examples: function foo() … Read more