What is the process for retrieving object element information from a web worker?

I'm currently diving into the realm of web workers and need to offload some heavy computation tasks without blocking the main browser thread.

At the moment, I have an AJAX call that fetches an XML data structure with multiple data blocks structured like this:

<data>
   <sub1>
   <sub2>
   <sub3>
</data>
<data>
   <sub1>
   <sub2>
   <sub3>
</data>

Next, I convert this structure into a JavaScript object using the following code:

var node = $(xml).find(data);

Afterwards, I serialize the object for transfer to the worker as shown below:

var toPass = JSON.stringify(node);

Subsequently, I send the variable (toPass) to the worker in this manner:

worker.postMessage(toPass);

Everything seems to be running smoothly up until this point. However, I've encountered difficulties when attempting to access the data within the worker.

Inside the worker function, I make an effort to parse the received data like so:

onmessage = function (oEvent) {

   var node = JSON.parse(oEvent.data);

   for(var i = 0; i < node.length; i++){

               var sub1 = node[i].find('sub1').text();         

   }    

};

The primary issue arises when trying to retrieve the "sub1," "sub2," and "sub3" data elements.

It's clear to me that my approach to accessing the data is flawed, particularly with my usage of XML.find method after parsing to a JSON object.

Could someone guide me on the correct way to access the data elements within "node[i]"?

Thanks in advance!

Answer №1

Lesson learned: never assume anything.

While working on this task, I made a mistake by assuming that the code var node = $(xml).find('data'); would return an array of objects with sub tags within each tag. However, it actually returned an array with empty objects, causing issues when trying to access the data in the web worker.

To fix this issue, I added a loop to parse the XML file before sending the required data to the worker:

var node = $(xml).find('data');

var nodeArray = [];

for (var i=0; i<node.length; i++){  

    var sub1    = $(node[i]).find('sub1').text();
    var sub2    = $(node[i]).find('sub2').text();
    var sub3    = $(node[i]).find('sub3').text();

    var jsonObj = {'sub1':sub1,'sub2':sub2,'sub3':sub3};

    nodeArray.push(jsonObj);              
}

worker.postMessage(nodeArray);

This way, no additional parsing is needed as the worker can handle arrays directly.

In the worker, I accessed the data like this:

onmessage = function (oEvent) {

var nodeArray = oEvent.data;

   for(var i = 0; i < nodeArray.length; i++){

       var sub1     = nodeArray[i].sub1;
       var sub2     = nodeArray[i].sub2;
       var sub3     = nodeArray[i].sub3;

   }

};

With this setup, I can efficiently process the data and optimize browser performance.

Now, I just need to finish processing the data and find a way to return it.

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