Callback

Callback = the primitive mechanism: you pass a function f to another function so f is called back later when the result is ready; control flow is still single-threaded but you must manually nest/chain these handlers (“callback hell”).

In JavaScript, a function is a special kind of object/ data type which you can pass as an argument. This is one of the most useful features of JavaScript programming language. When you call a function and you do not know when that function will return required result. Here you can pass a callback, which can be call when the result will come.

• Any function that is passed as an argument is called a callback function.
• In JavaScript, functions are objects. So functions can take functions as arguments, and can be returned by other functions. These functions are called higher-order functions.
• Callbacks are a way to make sure certain code doesn’t execute until other code has already finished execution.

var ifElse = function(condition, isTrue, isFalse) {
   if (condition) {
      return isTrue();
   }
   else {
      return isFalse();
   }
};

ifElse(true, function() { 
   console.log(true); 
}, function() { 
  console.log(false); 
})