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JavaScript: Experimenting with Conditional Statement

When conditional statement in your application grow to 30 lines or more, then it’s time for code refactoring. Conditional statements are un-avoidable but JavaScript functional programming behavior gives you really good way to handle such kind of scenario. 

Just take a scenario where you have to write a function which return sound for the given animal.

var soundOf = function(animal){
 var sound;
 if(animal === 'dog'){
  sound = 'bark';
 } else if(animal === 'duck'){
  sound = 'quack quack';  
 } else if(animal === 'owl'){
  sound = 'hoot';  
 } else {
  sound = 'animal not found!!!';
 }
 return sound;
}

Now think, what your code look like when you have to support 100 animal !!!
And same will be true for switch-case statement

var soundOf = function(animal){
 var sound;
 switch(animal){
  case 'dog': 
   sound = 'bark'; 
   break;
  case 'duck': 
   sound = 'quack quack'; 
   break;
  case 'owl': 
   sound = 'hoot'; 
   break;
  default: 
   sound = 'animal not found!!!';
 }
 return sound;
}

Here is my preferred way to write same function

var soundOf = function(animal){
 var animalSound = {
   dog: 'bark',
   duck: 'quack quack',
   owl: 'hoot' 
  },
  animalNotFound = 'animal not found!!!';
 
 return (animalSound[animal] || animalNotFound);
};

It’s look very clean and easy to understand. You can easily update this function with minimal changes to support more animals.

Ouput:

soundOf('dog');  //'bark'
soundOf('owl');  //'hoot'
soundOf('tiger'); //'animal not found!!!'
soundOf('duck'); //'quack quack'

You can use same pattern for some more complex task

var format = function(){
 function dateFormatter(value) {
  //code to format date
  return 'date: ' + value;
 }
 function numberFormatter(value) {
  //code to format number
  return 'number: ' + value;
 }
 function stringFormatter(value) {
  //code to format string
  return 'string: ' + value;
 } 
 function formatterNotFound(){
  return 'un-known data type!!!';
 }
 
 var formatterMapping = {
  date : dateFormatter,
  number : numberFormatter,
  string : stringFormatter 
 };
 
 return function(type, value){
  return (formatterMapping[type] || formatterNotFound)(value);
 };
}();

Output:

format('date','19-03-2012')  //'date: 19-03-2012'
format('number','123')   //'number: 123'
format('float','321.123')  //'un-known data type!!!'

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