USING UNDERSCORE.JS

jquery doesn't provide a lot of utility methods for other purposes.

small library   approximately 60 methods that can make your Javascript  easier to understand and more compact.

Accessing Underscore

underscore character  _

function or object-oriented style

_.isString(myVar)

_(myVar).isString();

the OO method first calls the underscore on the target (much like jquery does with selectors)

and then calls the methods on the resulting object.

Working with Collections

the bulk of the methods in Underscore.js are targeted at working with collections

where they are arrays or objects.  Because much of what you do in game developments is the manipulations of lists of objects such as sprites, these methods come in hnandy.

for(var i=0, len= sprites.length;i<len;i++) {

　　sprites[i].update();

}

_(sprites).invoke('update');

shorter and clearer about the intention of the code.

the only downside is that there is some overhead involved in calling an Underscore method

instead of just writing your own loop.

this overhead is negligible, and the advantage of smaller, more compact code

iw worth the trade-off.

 _.each(list,callback,[context])

Calls back each element of the list as an argument to the callback

use the native forEach in the browsers that support it.

context  object that is bound to this inside the callback.

_.map(list,callback,[context]) takes the return values from the callbback

mthod and returns a new array

_filter(list,callback,[context]) Similar to _.find except that it returns an array 

of all the items for which the callback returns true;

_without(array,[*array])  Returns a new array without any instances of values

removed;

_.uniq(array, [isSorted],[iterator])   _.uniq returns a copy of an array

with any duplicate elemnts removed.  sorted state  true to isSorted to improve 

performance

Using Utility Functions

_.bindAll(object,[*methodNames])

Modifies any calls to methodNames on object so that the context 

is always object.

_.keys(object) / _.values(object)    Return all of an object's keys or values

_extend(destination,*sources)  Copies all the properties from a list

of source objects over to the destination, overwriting any existing 

properties.

_.is(ObjectType)   check the type of a passed-in object. this 

is useful beacuse JS does.nt provide built-in checking methods

_.isEqual, _.isEmpty,  _.isElement,_.isArray, _.isFunction,_.isString,

_isNumber,_.isBoolean,_isNaN, _.isNull, and _.isUndefined,  

_uniqueId([prefix]) generates a globally unique identifier for client-side

DOM elements  or models 

Chaining Underscore Method Calls

_(_(_(sprites)

　　.filter(function(s) {return s.category == "enemy";}))

　　.pluck('y'))

　　.max();

_.chain(sprites)

　　.filter(function(s){return s.category == "enemy";})

　　.pluck('y')

　　.max().value();