I found their job posting online and was emailed a coding challenge a few days later. You were given three hours to complete the following problem:

You must hit a unique API to receive JSON data, modify and analyze the data, and then generate JSON in a specific format and post the data back to a different URL. If the data was formatted correctly, it responded with a 200 and you were told to zip up your code and upload it.

After the coding challenge, I was asked to schedule a phone screen with a recruiter. They asked common questions about my experience, why HubSpot, why [company name], etc.

At the end of the phone screen, I was told the next step, if I made it, would be a final round on-site interview, and that they would let me know of their decision in a week or so.

I ended up getting to the final round interview. It was four parts:

• The first part was a tour of their office.
• The second was a technical interview with a CS question about n-grams that could be programmed in any language of my choosing.
• The third interview was half behavioral, half JavaScript-specific, focusing on prototype inheritance, closures, etc.
• The last section was a wrap-up about my interview experience and any suggestions, salary expectations, other outstanding offers, etc.

A few days later, I was given a phone call and received an offer that exceeded my expectations.

Given a string s and a number n, return the most common n-gram in s.

If I would like to add a function to the string prototype, how would I do it?