如何计算数组中对象键的总和

一个简单的循环

var a = [{level:1},{level:2},{level:3},{level:4}],        total = 0;    for (var i=0; i<a.length; i++) {        total += a[i].level;    }console.log('total', total)

或减少

var a = [{level:1},{level:2},{level:3},{level:4}]console.log(a.reduce( function(cnt,o){ return cnt + o.level; }, 0))