1 files changed, 56 insertions, 0 deletions
diff --git a/lib/persistent-page-mod.js b/lib/persistent-page-mod.js
new file mode 100644
index 0000000..5c00a8f
--- /dev/null
+++ b/lib/persistent-page-mod.js
@@ -0,0 +1,56 @@
+var timer = require("timer");
+
+function PersistentPageMod(window, callback) {
+  memory.track(this);
+  this.window = window;
+  this.callback = callback;
+  this.window.addEventListener("unload", this, false);
+  this.window.addEventListener("DOMSubtreeModified", this, false);
+  this.doMod();
+  require("unload-2").ensure(this);
+}
+
+PersistentPageMod.prototype = {
+  REPLACE_DELAY: 100,
+  doMod: function doMod() {
+    try {
+      this.callback.call(undefined, this.window);
+    } catch (e) {
+      console.exception(e);
+    }
+    this.timerID = null;
+  },
+  handleEvent: function handleEvent(event) {
+    switch (event.type) {
+    case "unload":
+      if (event.target == this.window.document)
+        this.unload();
+      break;
+    case "DOMSubtreeModified":
+      if (this.timerID == null) {
+        // Wait a bit to do the replacing. Otherwise, we just get called
+        // tons of times in a tiny period and end up hanging the browser
+        // for a while.
+        var self = this;
+        this.timerID = timer.setTimeout(function() self.doMod(),
+                                        this.REPLACE_DELAY);
+      }
+      break;
+    }
+  },
+  unload: function unload() {
+    if (this.timerID != null) {
+      timer.clearTimeout(this.timerID);
+      this.timerID = null;
+    }
+    this.window.removeEventListener("DOMSubtreeModified", this, false);
+    this.window.removeEventListener("unload", this, false);
+  }
+};
+
+require("errors").catchAndLogProps(PersistentPageMod.prototype,
+                                   "handleEvent");
+
+var register = exports.register = function register(window, callback) {
+  new PersistentPageMod(window, callback);
+};