oneatatime:在完成之前不要再次执行异步函数（WIP）

一次一个 我做这个是因为我需要这样的东西： var sync = oneAtATime ( function ( done ) { ajaxPost ( '/sync' , { data : data } , function ( err , res ) { // ... done ( ) ; } ) ; } ) ; sync ( ) ; // kicks off an AJAX request sync ( ) ; // does nothing because the AJAX request is still going // time passes and AJAX request completes sync ( ) ; // kicks off a new AJAX request because the previous one comple