When to use Closure in JavaScript

Here is when and how..

Problem to solve – find if an element exists in an array.

Bad code 1 – clutter global namespace

var names = ['Honda', 'BMW', 'Kia', 'Toyota']; var findIfCarMakeIsInList = function(make) {   return names.indexOf(make) > -1 ; } alert('Is Honda in list ->' + findIfCarMakeIsInList('Honda')); alert('Is Acura in list ->' + findIfCarMakeIsInList('Acura'));

Bad code 2  - slow because of initialization of local list every time method is call

var findIfCarMakeIsInList = function(make) {   var names = ['Honda', 'BMW', 'Kia', 'Toyota'];   return names.indexOf(make) > -1 ; } alert('Is Honda in list ->' + findIfCarMakeIsInList('Honda')); alert('Is Acura in list ->' + findIfCarMakeIsInList('Acura'));

Closure helps us to

1.       Avoid polluting global namespace

2.       And get the benefit of global objects.

var  FindIfCarMakeIsInList = function() { var names = ['Honda', 'BMW', 'Kia', 'Toyota']; // it will be initialized only once. // return function reference so that if can be called. return function(make) {       return names.indexOf(make) > -1 ; }; }(); alert('Is Honda in list ->' + FindIfCarMakeIsInList('Honda')); alert('Is Acura in list ->' + FindIfCarMakeIsInList('Acura'));

Thanks

Pradeep

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