sumBy 数字运算符

_ = require('lodash');
//var async = require('async');
//var asyncSave = require('asyncSave');


var objects = [{ 'n': 4 }, { 'n': 2 }, { 'n': 8 }, { 'n': 6 }];
 
let a = _.sumBy(objects,function(o){ return o.n })
console.info(a)// 20

let b = _.sumBy(objects,'n')
console.info(b)// 20