aggregate - Unable to make native javascript reduce() function work -

i'm trying aggregate data using reduce() function in javascript (similar this question):

html

product 1: <button id="product1">add one</button> product 2: <button id="product2">add one</button> 

js

$('button').on('click', function() {             var pid = $(this).attr('id');              cart[cart.length] = {id:pid, qty:1}              var result = cart.reduce(function(res, obj) {                     if (!(obj.id in res))                         res.__array.push(res[obj.id] = obj);                     else {                         res[obj.id].qty += obj.qty;                     }                     return res;                 }, {__array:[]})              console.log(result)     }); }); 

i'm unable make work array being return doesn't contain qty data. e.g.:

object {__array: array[1], product1: object} object {__array: array[1], product1: object} object {__array: array[2], product1: object, product2: object} 

the result i'm looking more like:

object {product1: 1}   //click on product1, quantity = 1 object {product1: 2}   //click on product1 again, quantity = 1 + 1 = 2 object {product1: 2, product2: 1}  //click on product2 

what missing?

http://jsfiddle.net/c4wug/4/

if want output object {product1: 2, product2: 1} , using reduce method, try below . passing initial value {}

reduce method syntax like

[].reduce(    function( previousvalue, currentvalue, index,  array ){},    initialvalue  ); 

and our solution

var cart = [];  $(document).ready(function(){       $('button').on('click', function() {              cart.push( { id:$(this).attr('id'), qty:1 } );              var result = cart.reduce(function(res, obj) {                  if (!(obj.id in res )) {                     res[obj.id] = 0                 }                       return ( res[obj.id] += obj.qty ) && res ;               }, {} )              console.log( result )     }); }); 

and fiddle http://jsfiddle.net/c4wug/8/