javascript-callbacks.js

/**
 * This function provides 2 callback functions - before and after.
 * `runBefore` is called beforer executing the thousand lines of code and
 * `runAfter` is called after executing the thousand lines of code.
 */
function functionThatDoesSomething( name, runBefore, runAfter ) {

	/**
	 * It is important to check the type else it will throw an error.
	 */
	if ( 'function' === typeof runBefore ) {
		runBefore( name );
	}

	/**
	 * Some thousands line of code
	 * .
	 * .
	 * .
	 * .
	 * .
	 */

	/**
	 * It is important to check the type else it will throw an error.
	 */
	if ( 'function' === typeof runAfter ) {
		runAfter( name );
	}
}

/**
 * Now you can provide your own callback functions, they can be named or anonymous.
 */
functionThatDoesSomething( 'Kaavya', greet, informEnd );

/**
 * This will be called in place of `runBefore` at line 13.
 *
 * The value of `someVar` will be `name` because that is what
 * is passed at line 13.
 */
function greet( someVar ) {
	console.log( 'Welcome ' + someVar + '!' );
}

/**
 * This will be called in place of `runAfter` at line 29.
 *
 * The value of `someVar` will be `name` because that is what
 * is passed at line 29.
 */
function informEnd( somevar ) {
	console.log( 'The function finished executing, what next ' + somevar + '?' );
}

/**
 * This file starts executing at line 36.
 *
 * 36: `functionThatDoesSomething` is called with 3 arguments: 'Kaavya', greet function, informEnd function.
 * 12: Checks if `runBefore` is a function, which is true because we passed `greet` function to it. It calls runBefore and passes it `name`
 * 44: console.logs at line 45
 * 16-27: Executes these lines
 * 28: Checks if `runAfter` is a function, which is true because we passed `informEnd` function to it. It calls runAfter and passes it `name`
 * 54: console.logs at line 55
 */