Avoid multiple callbacks, node. js Async Module Async Early Use

Originally wrote a paged query, callback several layers.

Exports.list =function(req,res) {varparams = {}; varCurrent_page = Common_util.get_param_value (req, ' current_page ', ' number ', 1); varPage_size = Common_util.get_param_value (req, ' page_size ', ' number ', 10); varStart_index =Common_util.get_start_index (current_page,page_size); Topic.find (params). Skip (Start_index). Limit (page_size). Sort ({' Reply_time ': -1}). EXEC (function(err,docs) {if(Err) {console.error (err); }Else{topic.count (params,function(err,count) {if(Err) {console.error (err); }Else{Docs.foreach (function(DOC) {Doc.interval=Date_util.interval (doc.last_reply_time);                    }); Category.find ({},function(Err, categorylist) {if(Err) {console.error (err); } Else {                            varresult = {}; Result.current_page=Current_page; Result.page_size=page_size; Result.total_count=count; Resutl.total_page=common_util.get_total_page (count,page_size); Result.datas=docs; Result.categorylist=categorylist; Console.dir ("Hello");                            Console.dir (result); Res.render (' Index ', result);                }                    });        }            }); }        });}

After using async, the code looks like this:

Exports.list =function(req,res) {varparams = {}; varCurrent_page = Common_util.get_param_value (req, ' current_page ', ' number ', 1); varPage_size = Common_util.get_param_value (req, ' page_size ', ' number ', 10); varStart_index =Common_util.get_start_index (current_page,page_size); Async.Parallel ({datas:function(CB) {topic.find (params). Skip (Start_index). Limit (page_size). Sort ({' Reply_time ': -1}). EXEC (function(Err,docs) {CB (ERR,DOCS);       }); }, Total_count:function(CB) {Topic.count (params,function(Err,count) {CB (ERR,COUNT);       }); }, CategoryList:function(CB) {category.find ({},function(Err, categorylist) {CB (err,categorylist);       }); }    },function(err,results) {if(Err) {console.error (err); }Else{results.current_page=Current_page; Results.page_size=page_size; Results.total_page=common_util.get_total_page (results.total_count,page_size); Res.render (' Index ', results); }    });}

Async.Parallel, parallel execution. Supports JSON formatting tasks, the returned data is also in JSON format, and the order of JSON fields is sorted by task field.

{datas:[{_id:539c156dce6d3ea40f1f1d15,Author: ' Yekai ',content: ' <p>\n\t<span style= "font-family: Microsoft Jacob Black, Tahoma, Verdana, Arial Font-size:16px;line-height:26px;background-color: #FFFFFF;" > Because the site has just been created, and does not provide any special content, only the official homepage of the content is translated, but also a part of the error, but believe that the site will become an understanding of Ubuntu in China's dynamic window. </span>\n</p>\n<p>\n\t<span style= "font-family: Microsoft Jacob Black, Tahoma, Verdana, song body; font-size:16px; Line-height:26px;background-color: #FFFFFF; " ><br/>\n< /span>\n</p> ',Category: ' Other ',title: ' Ubuntu China website is now available ',__v:1,Last_reply_time:tue June21:54:33 gmt+0800 (China Standard Time),last_reply_username: ' Yekai ',Reply_amount:2,      },{_id:53a04500e5cb4710178753a5,last_reply_username: ' Yekai ',Last_reply_time:tue June21:44:52 gmt+0800 (China Standard Time),Author: ' Yekai ',content: ' Bet lost ',Category: ' World_cup ',title: ' Germany won ',__v:2,Reply_amount:3,      },{_id:539c16fe9e359e841cc1b097,Author: ' Yekai ',content: ' <p>\n\t<span style= "COLOR: #434343; font-family: Microsoft Ya-hei, Tahoma, Verdana, Arial Font-size:16px;line-height:24px;background-color: #FBFBFB;" > According to foreign media reports, researchers ' latest research shows that the Earth's largest aquifer is located beneath the U.S. mantle layer, about 643.7 kilometres (400 miles) underground. </span>\n</p>\n<p>\n\t<span style= "color: #434343; font-family: Microsoft Jacob Black, Tahoma, Verdana, song body; Font-size:16px;line-height:24px;background-color: #FBFBFB; " ><br/>\n< /span>\n</p> ',Category: ' Other ',title: ' The Earth's largest reservoir ' found 643.7 km underground,__v:2,Last_reply_time:tue June22:06:43 gmt+0800 (China Standard Time),last_reply_username: ' Afei ',Reply_amount:3,       } ],Total_count:3,categorylist:[{_id:5397181a1f7f534418cbbd84,Desc: ' Java class ',code: ' Java ',name: ' Java ',__v:0},{_id:53971d90e209ea6414b2819f,desc: ",code: ' Nodejs ',name: ' Nodejs ',__v:0},{_ID:5399B429A068211816605FBB,desc: ",code: ' World_cup ',name: ' World Cup ',__v:0},{_ID:539C1526CE6D3EA40F1F1D14,desc: ",code: ' Other ',name: ' Other ',__v:0}],Current_page:1,page_size:10,Total_page:1}