javascript同数组里的对象比较，相等的话对象里的值累加。

Question

var arr = [{"code":"111","num":1},{"code":"112","num":1},{"code":"111","num":3},{"code":"113","num":1},{"code":"113","num":5},{"code":"111","num":1}]//像这样的一个数组，比较对象code，如果相等，取其num相加的值输出。