How to get dynamic element HTML use Addon SDK with Timers? - firefox-addon-sdk

Question

I want to scrape a page, the HTML content of this page auto change in a time frame. So i want to use pageMod and Timers of Addon Sdk to get the element innerHtml which change often.
Here are my scripts :
In main.js :
var tag = "container1";
var data = require("sdk/self").data;
var pageMod = require("sdk/page-mod");
var timer = require("sdk/timers");
var i = 0;
function scrapeData()
{
i = i + 1;
console.log("Begin pageMod : " + i);
pageMod.PageMod({
include: "*.test.com",
contentScriptFile: data.url("element-getter.js"),
contentScriptWhen: 'ready',
onAttach: function(worker) {
worker.port.emit("getElements", tag);
worker.port.on("gotElement", function(elementContent) {
console.log(elementContent);
});
}
});
console.log("End pageMod : " + i);
}
timer.setInterval(scrapeData, 10000);
And in data/element-getter.js :
self.port.on("getElements", function(tag) {
var elements = document.getElementById(tag);
self.port.emit("gotElement", elements.innerHTML);
});
After install this Firefox Add-on, when timers is running, it can only get the innerHtml one time, and the other time, it only display Begin pageMod and End pageMode in console log. Please help.

Answer 1

What you're currently doing is attaching the same page mod multiple times.
What you should do is move the timer inside the content script:
data/element-getter.js:
function scrapeData() {
var elements = document.getElementById(tag);
self.port.emit("gotElement", elements.innerHTML);
}
setInterval(scrapeData, 10000);
If you really want to keep the timer in the main page, then you need to maintain an array of worker instances, and loop through this array to emit your custom event. See this answer for more details.
(PS. Depending on your use case, the sdk/frame/hidden-frame module might be of interest.)