Understanding callback functions in Javascript

Callback

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// define our function with the callback argument
function some_function(arg1, arg2, callback) {
  // this generates a random number between
	// arg1 and arg2
	var my_number = Math.ceil(Math.random() *
		(arg1 - arg2) + arg2);
	// then we're done, so we'll call the callback and
	// pass our result
	callback(my_number);
}
// call the function
some_function(5, 15, function(num) {
	// this anonymous function will run when the
	// callback is called
	console.log("callback called! " + num);
});
/It might seem silly to go through all that trouble when the value could just be returned normally, but there are situations where that’s impractical and callbacks are necessary.