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Don’t reinvent the wheel: Some useful JS libraries


It is very common to see “Utility” file in many project, which have all commonly used functions. In other word you can say it is kitchen sink file, where people dump all common functions. Before you realize it grows more than 1000 lines and become a maintenance hell.

So keep in mind, each time when you write a new class or function you are increasing the project maintenance coast.


There are few things you should consider before writing the code

  • Know Your Library – Most of the library has some utility functions so keep exploring it.
  • Use Utility Library – If existing library doesn't have needed functionality then always consider using 3rd party Utility Library with good test converge.


Some of my favourite libraries


Underscore JS 

It is one of the best utility library, which has collection of most commonly used functions. Here are few function with example code.



_.each([1, 2, 3], function(num){ alert(num); });
=> alerts each number in turn...
_.each({one : 1, two : 2, three : 3}, function(num, key){ alert(num); });
=> alerts each number in turn...

Map[1, 2, 3], function(num){ return num * 3; });
=> [3, 6, 9]{one : 1, two : 2, three : 3}, function(num, key){ return num * 3; });
=> [3, 6, 9]


var evens = _.filter([1, 2, 3, 4, 5, 6], function(num){ return num % 2 == 0; });
=> [2, 4, 6]


var stooges = [{name : 'moe', age : 40}, {name : 'larry', age : 50}, {name : 'curly', age : 60}];
_.pluck(stooges, 'name');
=> ["moe", "larry", "curly"]


_.union([1, 2, 3], [101, 2, 1, 10], [2, 1]);
=> [1, 2, 3, 101, 10]


_.intersection([1, 2, 3], [101, 2, 1, 10], [2, 1]);
=> [1, 2]


_.keys({one : 1, two : 2, three : 3});
=> ["one", "two", "three"]


_.values({one : 1, two : 2, three : 3});
=> [1, 2, 3]


_.escape('Curly, Larry & Moe');
=> "Curly, Larry & Moe"


var stooges = [{name : 'curly', age : 25}, {name : 'moe', age : 21}, {name : 'larry', age : 23}];
var youngest = _.chain(stooges)
  .sortBy(function(stooge){ return stooge.age; })
  .map(function(stooge){ return + ' is ' + stooge.age; })
=> "moe is 21"

and more

var lyrics = [
  {line : 1, words : "I'm a lumberjack and I'm okay"},
  {line : 2, words : "I sleep all night and I work all day"},
  {line : 3, words : "He's a lumberjack and he's okay"},
  {line : 4, words : "He sleeps all night and he works all day"}

  .map(function(line) { return line.words.split(' '); })
  .reduce(function(counts, word) {
    counts[word] = (counts[word] || 0) + 1;
    return counts;
}, {}).value();

=> {lumberjack : 2, all : 4, night : 2 ... }


Below is the complete list of functions provided by this library.  








each first bind keys noConflict chain
map initial bindAll values identity value
reduce last memoize functions times  
reduceRight rest delay extend mixin  
find compact defer pick uniqueId  
filter flatten throttle defaults escape  
reject without debounce clone result  
all union once tap template  
any intersection after has    
include difference wrap isEqual    
invoke uniq compose isEmpty    
pluck zip   isElement    
max indexOf   isArray    
min lastIndexOf   isObject    
sortBy range   isArguments    
groupBy     isFunction    
sortedIndex     isString    
shuffle     isNumber    
toArray     isFinite    
size     isBoolean    



Date JS 

This is very fluent JS library for date and really easy to use.


date comparison

var temp = new Date();
var today = new Date(someDate.getTime()); 
var today.setHours(0);
var today.setMinutes(0);
var today.setSeconds(0);
var today.setMilliseconds(0);
(today == temp); // true|false


date comparison with date JS

/ with Datejs, but without .same
// New
// Or,;


more example

var today =;
var past =;
var future =;, future);                    // -1, new Date().clearTime());    // 0, past)                       // 1


Date formatting [formatting options]

new Date().toISOString();  // ""2008-04-13T10:07:15Z""

new Date().toString("yyyy-MM-ddTHH:mm:ssZ");  // "2008-04-13T04:11:05Z";           // native .toString() functionality"M/d/yyyy"); // 11/19/2007"d-MMM-yyyy"); // 19-Nov-2007

new Date().toString("HH:mm");      // 18:45


Please check this wiki page for more information about this library.

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