How to Fix Googlebot Causing JavaScript Errors

If you’ve ever checked your website logs or Google Search Console reports, you might have seen JavaScript errors coming from Googlebot, especially errors like:

Error Observed

Uncaught ReferenceError: myFunction is not defined

I ran into this exact problem recently, and I want to share what I learned—why Googlebot causes these errors, how my code was structured, what the issue really was, and how I fixed it with some added improvements.

My Code

Here’s the basic setup I had on my website:

HTML part:

<script type="text/javascript" src="https://example.com/js/my-script.js?v=1.4"></script>

<script>
    $('document').ready(function(){
        if (typeof myFunction != 'undefined') {
            myFunction.init();
        }
    });
</script>

And inside my-script.js:

var myFunction = (function () {
    var init = function () {
        // do stuff
    };

    return { init: init };
})();

What Is This Code Doing?

• The external JavaScript file my-script.js defines a variable myFunction as an Immediately Invoked Function Expression (IIFE). This pattern creates a private scope and exposes just the init method publicly.
• In the inline script, I want to make sure that before I call myFunction.init(), the variable myFunction actually exists. So, I check with typeof myFunction != 'undefined' which is a safe way to see if something is defined or not.
• I wrapped this call inside a jQuery document ready handler, so the code runs once the DOM is fully loaded.

Does It Work Fine for Most Browsers But Not for Googlebot?

In normal browsers, this works without any issues:

• The external script loads fully.
• myFunction is globally available.
• The inline script runs after the DOM is ready, finds myFunction defined, and calls init().

But Googlebot’s JavaScript execution is different:

• Googlebot Sometimes Doesn’t Run JS Fully or Delays It
  Googlebot can delay or skip executing external JavaScript files for faster crawling. If the bot hasn’t loaded my-script.js when the inline script runs, myFunction won’t exist yet.
• Order of Execution May Differ
  Unlike browsers, the bot might process the inline script before the external one, so the typeof check might not protect against an earlier reference somewhere else.
• Googlebot Uses Different User Agent and Behaviors
  The bot mimics mobile browsers or headless environments that can block or ignore certain scripts.
• Access Restrictions or Network Issues
  If robots.txt, CORS, or network problems block the external JS from loading, the bot never sees myFunction.

Why Does the typeof Check Fail

Normally, typeof myFunction != 'undefined' should never throw an error, even if myFunction doesn’t exist. The typeof operator is designed to be safe.

So, if you’re seeing a “not defined” error, possible reasons include:

• Somewhere else in your code (or third-party scripts) using myFunction without a typeof check first.
• A typo in your jQuery ready handler:
  Notice the code uses $('document').ready() but it should be $(document).ready(). The former selects a literal <document> element (which doesn’t exist), so the handler may never fire, causing unexpected behavior.
• The bot may execute scripts in an unexpected order, or some asynchronous behavior breaks assumptions.

How I Fix and Improve the Code

Here’s the revised, safer version I implemented.

Correct the jQuery

$(document).ready(function(){
    if (typeof myFunction !== 'undefined' && myFunction && typeof myFunction.init === 'function') {
        myFunction.init();
    }
});

This ensures:

• Correct syntax for the ready handler.
• Checking not just if myFunction exists, but also if myFunction.init is a function before calling it.

Add a Fallback For When myFunction isn’t Ready

$(document).ready(function(){
    if (typeof myFunction !== 'undefined' && myFunction && typeof myFunction.init === 'function') {
        myFunction.init();
    } else {
        console.warn('myFunction is not defined or init method missing');
        // You can add fallback code here if needed
    }
});

This logs a warning so you can easily spot if your function is missing.

Handle Asynchronous Loading Safely

Sometimes scripts load asynchronously and may not be ready when your inline script runs. To handle this, I implemented a queue to hold calls until the script loads:

// Initialize a queue to store calls before myFunction is ready
window.myFunctionQueue = window.myFunctionQueue || [];

function callMyFunctionInit() {
    if (typeof myFunction !== 'undefined' && myFunction && typeof myFunction.init === 'function') {
        myFunction.init();
    } else {
        // Queue the call for later if myFunction is not ready yet
        window.myFunctionQueue.push('init');
    }
}

$(document).ready(function(){
    callMyFunctionInit();
});

// After my-script.js loads, process the queued calls
function drainMyFunctionQueue() {
    if (window.myFunctionQueue.length > 0) {
        window.myFunctionQueue.forEach(function(method){
            if (typeof myFunction[method] === 'function') {
                myFunction[method]();
            }
        });
        window.myFunctionQueue = [];
    }
}

Then, in my-script.js, I added this at the end:

myFunction = (function () {
    var init = function () {
        // do stuff
    };

    // After defining myFunction, process any queued calls
    if (window.drainMyFunctionQueue) {
        window.drainMyFunctionQueue();
    }

    return { init: init };
})();

// Expose the queue draining function globally
window.drainMyFunctionQueue = function() {
    if (window.myFunctionQueue && window.myFunctionQueue.length > 0) {
        window.myFunctionQueue.forEach(function(method){
            if (typeof myFunction[method] === 'function') {
                myFunction[method]();
            }
        });
        window.myFunctionQueue = [];
    }
};

Final Thoughts

Dealing with JavaScript errors caused by Googlebot can be tricky because its environment differs from typical browsers. This means code that works perfectly on your desktop or mobile browser may throw errors or behave unexpectedly when crawled.

Here’s what I learned:

• Always use typeof checks before referencing variables that may not yet exist.
• Be mindful of the order in which your scripts load. Async loading can break assumptions.
• Double-check syntax, especially for event handlers like jQuery’s document ready. Small typos can cause big headaches.
• Implement fallback behaviors and queues for safer execution in uncertain environments.
• Test your site with tools like Google’s Search Console URL inspection, Mobile-Friendly Test, or even simulate Googlebot’s user agent to catch issues early.