A guide to hiring an RxJS developer
RxJS is a JavaScript library for reactive programming. It lets code treat clicks, typed text, server replies and live messages as streams of values over time. Used well, it keeps complicated async features short and orderly. Used badly, it creates bugs that are hard to trace. This guide explains what an RxJS developer does, when you need one and how to choose well. It helps founders, product owners and engineering leads whose apps have live data or tangled async code.
What an RxJS developer is responsible for
This developer designs how events and data flow through your app. When a user types in a search box, what should happen to the old request? When the server sends a new message, which screens should update? When a call fails, should the app retry or show a message? They write the streams that answer these questions, add tests and make sure each stream is closed when it is no longer needed. They also review code that others wrote and simplify it.
Why streams are worth the effort
Many app features are not a single request and a single answer. They are a series of events that overlap: typing while results load, a socket that reconnects, a button that must not be clicked twice. Promises handle one result well, but they do not cancel or repeat easily. Streams let a developer describe the whole behaviour in one place, with cancel, retry and timing built in. The price is that the team must understand the model, which is why an experienced person helps.
How this role differs from nearby roles
An Angular developer builds whole apps in that framework and uses RxJS as one of many tools, so choose that page when your main need is Angular screens, forms and routing. A JavaScript developer covers the browser, the server and often TypeScript. A React developer builds screens in React, and a Node.js developer works on the server. Use the RxJS page when streams and async flow are the heart of the job.
When an RxJS developer makes sense
- Your app has live data, such as a dashboard, a feed or chat.
- Search, filters or autosave fire too many requests or show old results.
- Your Angular code uses RxJS and nobody on the team feels sure about it.
- Screens slow down over time, which can point to streams that never close.
- You want tests for time-based features, such as delays and retries.
If your features are simple requests with single answers, a general developer and plain async functions may be enough.
What to look for in a background
Ask for examples where streams solved a real problem. A good answer names the feature, the bug or slowdown and how it was fixed and tested. Be careful with a long list of operators and no stories. Ask the person to sketch, on paper, how a search box should work from the first key press to the final result.
Interview questions to try
- When would you choose switchMap over mergeMap, and what goes wrong if you pick the other one?
- How do you make sure a stream stops when a screen is closed?
- What is the difference between a cold and a hot stream?
- How do you keep a stream alive when one request fails?
- How would you test a search box that waits for the user to stop typing?
Clear answers come with an example and plain words. Be careful with answers that sound memorised but cannot be applied to a small case.
A paid trial task
Pick a real feature from your app, such as search as you type or a live list. Ask each finalist to review the code, list the risks and fix one problem with a test. Pay for the time. You will see how they think, how carefully they test and how well they explain a tricky topic to a person outside engineering.
Match the person to the job
A new live feature needs someone who can design the flow from scratch. An older app with messy streams needs a careful reader who simplifies it step by step. A team that is new to RxJS needs a person who is happy to teach and to leave clear examples in the code. Ask each candidate which of these they have done.
Access and routine
Fix the weekly hours at the start and check them every few months. The engineer should have personal logins for the code host and test servers, and the company should own every account. A brief note with each change, saying how to undo it, helps later. End their access when the work finishes.
Working with the rest of your team
Tell the team which flows the engineer owns and share a short diagram of how data moves through the app. Agree simple rules, such as how streams are named and how they are closed. A weekly review of open changes catches mistakes early. Ask for a short guide with a few examples, so that new teammates can follow the same pattern.
Mistakes to avoid
- Using streams for simple requests that a promise would handle well.
- Forgetting to close streams, which slows pages over time.
- Stacking many operators into one long chain that nobody can read.
- Skipping tests for time-based features such as delays and retries.
Working mainly in a framework? See our Angular developers, or look at our JavaScript developers for a wider mix of skills.