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javascriptdojoevent-handlingpublishpublish-subscribe

Dojo publish - subscribe not working

The code below is a simple abstraction of what I want to do - it deals with publish and subscribe of the dojo event model. My aim is to publish an event, and subscribe a method to that event. 

<html> 
<head>
<script> 
dojoConfig={async:true, parseOnLoad: true}
</script>
<script type="text/javascript" src="dojo/dojo.js">
</script>
<script language="javascript" type="text/javascript">
require(["dojo/topic","dojo/domReady!"],

    function(topic){

    function somethod() {
        alert("hello;");
    }
    try{
        topic.publish("myEvent");
    }
    catch(e){
        alert("error"+e);
    }

    //topic.publish("myEvent");  
try{
topic.subscribe("myEvent", somethod);

}catch(e){alert("error in subscribe"+e);}
});
</script>
</head>
<body></body>
</html>

I get no alerts, not even in try and catch blocks. Developer console also shows no errors. Is this the correct way to handle publish and subscribe?

Solution

  • You're very close but have made one little mistake. You're subscribing to the topic after you're publishing to it, so you're not catching it. If you put the pub after the sub it'll work.

    Here's your sample with slight modifications and comments:

    <html> 
<head>
<script> 
dojoConfig={async:true, parseOnLoad: true}
</script>
<!-- I used the CDN for testing, but your local copy should work, too -->
<script data-dojo-config="async: 1"
        src="//ajax.googleapis.com/ajax/libs/dojo/1.10.4/dojo/dojo.js">
</script>
<script language="javascript" type="text/javascript">
require(["dojo/topic","dojo/domReady!"],
function(topic){

    function somethod() {
        alert("hello;");
    }
    try{
        topic.publish("myEvent");
        /* ignored because no one is subscribed yet */
    }
    catch(e){
        alert("error"+e);
    }

    try{
        topic.subscribe("myEvent", somethod);
        /* now we're subscribed */

        topic.publish("myEvent");
        /* this one gets through because the subscription is now active*/

    }catch(e){
        alert("error in subscribe"+e);
    }
});
</script>
</head>
<body></body>
</html>