Question

我正在学习javascript中的Promise api，并希望将其应用于以下内容：考虑以下使用Google Feed（来自http://www.javascriptkit.com/dhtmltutors/rssdisplayer.js）输出rss Feed内容的javascript代码

google.load("feeds", "1") //Load Google Ajax Feed API (version 1)

function rssdisplayer(divid, url, feedlimit, showoptions) {
    this.showoptions=showoptions || "" //get string of options to show                 ("date" and/or "description")
    var feedpointer=new google.feeds.Feed(url) //create new instance of Google Ajax Feed API
    feedpointer.setNumEntries(feedlimit) //set number of items to display
    document.write('<div id="'+divid+'">Loading feed...</div>')
    this.feedcontainer=document.getElementById(divid)
    var displayer=this
    feedpointer.load(function(r){displayer.formatoutput(r)}) //call    Feed.load() to retrieve and output RSS feed
}

rssdisplayer.prototype.formatdate=function(datestr){
     var itemdate=new Date(datestr)
     return "<span style='color:gray; font-size:    90%'>"+itemdate.toLocaleString()+"</span>"
}


rssdisplayer.prototype.formatoutput=function(result){
    if (!result.error){ //if RSS feed successfully fetched
      var thefeeds=result.feed.entries //get all feed entries as a JSON  array
      var rssoutput="<ul>"
      for (var i=0; i<thefeeds.length; i++){ //loop through entries
          var itemtitle="<a href=\"" + thefeeds[i].link + "\">" +             thefeeds[i].title + "</a>"
          var itemdate=/date/i.test(this.showoptions)?              this.formatdate(thefeeds[i].publishedDate) : ""
          var itemdescription=/description/i.test(this.showoptions)? "<br />"+thefeeds[i].content : /snippet/i.test(this.showoptions)? "<br />"+thefeeds[i].contentSnippet  : ""
         rssoutput+="<li>" + itemtitle + " " + itemdate + itemdescription + "</li>"
      }
     rssoutput+="</ul>"
     this.feedcontainer.innerHTML=rssoutput
  }
  else //else, output error
   alert("Error fetching feeds: "+result.error.message)
}

检索rss Feed并显示调用

new rssdisplayer("adiv", "somerssurl", 5, "date, description")

如何更改回调formatoutput以返回Promise (using say new Promise(function resolver...)并在创建rssdisplayer对象后使用它？目标是能够在Feed负载上进行同步，以便依赖于此的任务可以执行某些操作。

如何为javascript对象创建一个promise

0 个答案: