Why does the Selenium IDE recorder call my LocatorBuilder function multiple times per user click?

I have defined a LocatorBuilder function and inserted it as the first element of LocatorBuilders array. It is working nicely. However, when I add an alert() at the top of m开发者_StackOverflowy function, I observe that my function is being called twice for each user click that is recorded. Specifically, when I turn on recording and click a button on the page, the sequence of events is: 1) my function gets called, 2) the click is recorded utilizing the locator expression that I have produced, 3) the browser processes the click, 4) my function is called again.

Note - I can't find this documented anywhere, but I surmise that fundamentally, the recorder calls each function in the LocatorBuilders list, each returning a candidate locator expression, until it gets a non-null expression that matches exactly one element on the page.

So my function works as desired, but the extra function call seem redundant. Is there some valid reason that my expression builder function needs to be called more than once? For example, is it possible for the subject HTML element to change between calls? What is the recorder doing between successive calls to my function?

EDIT: DOH! I discovered that I was adding my function into the LocatorBuilders.order list twice. So now my function only gets called twice. Still though, why multiple calls?

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When you define a locator-builder via LocatorBuilders.add(name, func), Selenium adds the name to the global array: LocatorBuilders.order. The recorder iterates over these names on each user event, calling each builder function in turn.

Custom definition(s) are loaded into the IDE by configuring your script as either a "Core extension" or an "IDE extension". Both sets of extensions are loaded when the Selenium IDE window opens, (IDE then Core), so it might not seem to matter which one you specify. But beware that the Core extension scripts get reloaded the first time a command is played back in the IDE window. Therefore scripts that are configured as Core extensions need to be idempotent.

So since a locator-builder is Recorder functionality, configure it as an IDE extension and it will get loaded only once. If there is some reason it needs to coexist with runtime code, (shared logic is likely), you can load it as a Core extension, but make sure it is idempotent. (And it may as well be loaded only in the IDE.) For example:

if ("SeleniumIDE" in window) { // we're running in the IDE window
  var i = LocatorBuilders.order.indexOf(locatorName);
  if (i != -1)
    LocatorBuilders.order.splice(i, 1); // remove a previous entry
  LocatorBuilders.add(locatorName, function(elem) { ...
}

(Note that the indexOf() and splice() array methods are not supported by all browsers, but Firefox does, and this is IDE logic.)