优化thenAdd方法
优化thenAdd方法

lukw00/thinkjs,74sharlock/thinkjs,maxzhang/thinkjs,lukw00/thinkjs,akira-cn/thinkjs,Qihoo360/thinkjs,75team/thinkjs,akira-cn/thinkjs,75team/thinkjs,snadn/thinkjs,maxzhang/thinkjs,thinkjs/thinkjs,75team/thinkjs,maxzhang/thinkjs,akira-cn/thinkjs,74sharlock/thinkjs