无法将值存储在全局变量内

Question

I am reading a Rss feed using setInterval method and displaying notification to the users ,I want to make sure I store the latest feed title so that the user does not get multiple notification of the same title again. So I declare a global var global_Rsstitle at the top of my notification.js . Now I try to pass the value of entry_title to the global var the value is not being retained in the global var after the setinterval method is called. Is there a better way of storing the value of entry_title and checking each time the setInterval method is called so as to avoid multiple notification of the same title.

My notification.js

/** global variable **/

var global_Rsstitle;

/** end global variable **/
function get_rss1_feeds() {

    var Rss1_title = getRss("http://rss.cnn.com/rss/cnn_topstories.rss", function(entry_title) {
        if(global_Rsstitle != entry_title)
        global_Rsstitle = entry_title;
        console.log('test',global_Rsstitle); // the value is outputed but global var is not working
    });
console.log('test1',global_Rsstitle);   // outputted as undefined ??
    }

    google.load("feeds", "1");
    google.setOnLoadCallback(function () { setInterval(get_rss1_feeds, 5000); });

My jsRss.js file

function getRss(url, callback){
    if(url == null) return false;

    // Our callback function, for when a feed is loaded.
    function feedLoaded(result) {
        if (!result.error) {
            var entry = result.feed.entries[0];
            var entry_title = entry.title; // need to get this value
            callback && callback(entry_title);        
        }
    }
    function Load() {       
        // Create a feed instance that will grab feed.
        var feed = new google.feeds.Feed(url);
        // Calling load sends the request off.  It requires a callback function.
        feed.load(feedLoaded);      
    }    
    Load();             
}

Answer 1

You define a variable called global_Rsstitle; but in your code you use Rsstitle . They are two different things

Answer 2

Shouldn't you be setting global_Rsstitle and not Rsstitle ?

var global_Rsstitle;

/** end global variable **/
function get_rss1_feeds() {

    var Rss1_title = getRss("http://rss.cnn.com/rss/cnn_topstories.rss", function(entry_title) {
        if(global_Rsstitle!= entry_title)
        global_Rsstitle = entry_title;
        console.log('test',global_Rsstitle); // the value is outputed but global var is not working
    });   
}

UPDATE

You do realize that you cant use that variable until the response comes back, right?

In other words, you can't do this:

get_rss1_feed();
alert(global_Rsstitle);

because the alert will be trigger before the feed is read and the variable is assigned.. To make it worse, you're delaying the execution with your interval.

Answer 3

After your declaration of var global_Rsstitle; , you're never assigning anything to it. It needs to be on the LHS of some expression. Adding global_ to the variable doesn't make it global; defining it outside of a function does.