wrap a thunk to generator

thunk_wrapper.js

function wrapper ( process ) {
    var res=  [];
    var resolvers = [];

    var add_next = function() {
      res.push(new Promise(function( resolve, reject ) {
          resolvers.push({
            resolve,
            reject
          })
      }))
    }
    add_next();

    var j = 0;
    var callback = function( err, ret ) {
      if( err ){
        resolvers[j].reject(err);
      } else {
        resolvers[j].resolve(ret);
      }
      
      j ++;
       if(!resolvers[j]) {
           add_next();
       }
    }

    process(callback)

    var k = 0;
    var interator = {
      next () {
        var ret = res[k];
        if(!ret){
          add_next();
        }
        ret = res[k];
        k++
        return ret;
      }
    };

    return interator;
}