javascript - Promise is undefined -


i want change function using promise deal callback

the result of fatch this

[{ href: 'http:/segmentfault.com/q/1010000002714413',     title: 'js图片轮播' },   { href: 'http:/segmentfault.com/q/1010000002714953',     title: 'stackoverflow, segmentfault 之类的网站是如何实现在输入问题时，下方出现模糊搜索的结果提示？' },   { href: 'http:/segmentfault.com/q/1010000002711687',     title: 'js与局域网' } ]

at first time , use module "q" change function

function fatch(url) {      var deferred = q.defer();     superagent.get(url)         .end(function(err, data) {             if (err){                 console.log(err);                 deferred.reject(err);             }              var $ = cheerio.load(data.text);             var result = [];              $('.question-stream .stream-list__item').each(function(index, ele) {                 var $ele = $(ele);                 var href = path.join(url, $ele.find('.title a').attr('href'));                 var title = $ele.find('.title').text();                  result.push({                     href: href,                     title: title                 });             });              // console.log(result);             deferred.resolve(result)             return deferred.promise;          });  }

i expected can result "then"

fatch(url).then(console.log(data),console.log(err));

but i'm fail :

typeerror: cannot read property 'then' of undefined

and try way :

function fatch(url) {  var promise = new promise(); superagent.get(url)     .end(function(err, data) {         if (err){             console.log(err);             promise.reject(err);         }          var $ = cheerio.load(data.text);         var result = [];          $('.question-stream .stream-list__item').each(function(index, ele) {             var $ele = $(ele);             var href = path.join(url, $ele.find('.title a').attr('href'));             var title = $ele.find('.title').text();              result.push({                 href: href,                 title: title             });         });          // console.log(result);         promise.resolve(result)         return promise;      });  }

but didn't work before..

typeerror: promise resolver undefined not function

i changed function , it's working :

function fatch(url) {      var deferred = q.defer();     var result = [];     superagent.get(url)         .end(function(err, data) {             if (err) {                 console.log(err);             }             var $ = cheerio.load(data.text);               $('.question-stream .stream-list__item').each(function(index, ele) {                 var $ele = $(ele);                 var href = path.join(url, $ele.find('.title a').attr('href'));                 var title = $ele.find('.title').text();                  result.push({                     href: href,                     title: title                 });             });          });     // console.log(result);     deferred.resolve(result);      return deferred.promise;  }

and want result :

fatch(url).then(function(data){     console.log(data); },function(err){     console.log(err); });

i don't know why data [] ?

actually , it's first time use promise , i'm confusing , how use promise change function , please me , lot~

your third approach one, you're wrong when "resolve" deferred before returning promise. make resolved synchronously while should make in asynchronous code. solution mix between #1 try , #3 try :

function fatch(url) {      var deferred = q.defer();     superagent.get(url)         .end(function(err, data) {             if (err){                 console.log(err);                 deferred.reject(err);             }              var $ = cheerio.load(data.text);             var result = [];              $('.question-stream .stream-list__item').each(function(index, ele) {                 var $ele = $(ele);                 var href = path.join(url, $ele.find('.title a').attr('href'));                 var title = $ele.find('.title').text();                  result.push({                     href: href,                     title: title                 });             });              // console.log(result);             deferred.resolve(result);          });      return deferred.promise; }

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