Callback Function
- 1. What is a Callback Function? By Roland D. San Nicolas
- 2. Functions in Javascript Edited MDN definition = A “subprogram” that can be called by code externally or internally to the function. A function is composed of a sequence of statements called the function body. Values can be passed to a function, and the function will return a value. Functions are “First Class” objects which means functions have properties and methods (a function), and can be passed as arguments to other functions, return them as values from other functions, and can be assigned to variables. Functional Programming: improve code composition
- 3. A function declaration function helloWorld() { console.log(“Hello World”); } helloWorld();
- 4. A function expression (anonymous) function(x) { return //some value }; (x);
- 5. Callback Function Definition Wikipedia - “A reference to executable code, or a piece of executable code, that is passed as an argument to other code which is expected to call back (execute) the argument at some convenient time.” “Higher Order Function” = the hosting function “Callback function” = the function within the Higher Order Function. Javascript statements are performed sequentially (line by line). Callbacks are useful in performing its code at a specified time as to not block subsequent lines of code (Synchronous vs Asynchronous).
- 6. Asynchronous Programming Asynchronous programming = writing a program where a function(s) happen at some “later” point in time as to not “block” the rest of the code (improved end user experience). Common with jQuery and I/O programming (send/receive data from file systems and databases) used in Node.js.
- 7. jQuery Callback Function Example $(“btn1”).click(function(){ console.log(“Button 1 clicked”); });
- 8. Asynchronous Callback Function example request = prepare_the_request(); send_request_asynchronously(request, function (response){ display (response); }); //this code block returns immediately allowing subsequent code to continue (non-blocking). The function parameter will be called when the response is available.
- 9. Resources Javascriptissexy.com (Concise, good place to start) Javascript the Good Parts by Douglas Crockford Eloquent Javascript You-Dont-Know-JS: “Async & Performance” Mozilla Developer Network Youtube: especially the funfunfunction channel - “Higher-order functions” and “Learning Functional Programming with Javascript” by Anjana Vakil stackoverflow