The Tech Talks series brings you directly into the world of PayPay Group’s diverse product members, from nearly 50 countries and regions worldwide, sharing their approaches to product development and the atmosphere within their teams.
In this edition, we interviewed Fangjian Chen, an App Engineer at PayPay Card, about his efforts to improve the mini app’s speed and the growth he experienced through the project.
Fangjian Chen
Manager, Team 7, Growth Product Division, PayPay Card
I am Fangjian Chen from China. I came to Japan in 2015 and began my career at a System Integrator. Subsequently, I worked as an App Engineer at a major e-commerce site, primarily focusing on speed improvements. Having been a loyal user of PayPay Card for a long time, I was keen to contribute to its speed enhancement, which ultimately led me to join PayPay Card in July 2024.
Confidence in Mini App Speed Improvement
Could you tell us about your current role and mission?
I am part of the Growth Product Division at PayPay Card, where I focus on improving the speed of the PayPay Card mini app within the main PayPay app. My core mission is to significantly enhance the mini app’s display speed and elevate the user experience through architectural review, refactoring, and performance optimization. In parallel, I also serve as an Engineering Manager, and supporting the growth of my team members is another key part of my role.
What was your career path before joining PayPay Card?
After arriving in Japan in 2015, I began my career as an SIer. Seeking involvement in B2C services rather than B2B, I transitioned to a major venture company operating an e-commerce site. In my previous position, I was responsible for enhancing the speed of their online supermarket, and I’m proud to say I achieved significant results.
As a user, I frequently used PayPay-related services and was a heavy user. I had a strong personal attachment to PayPay Card, especially as it was my first credit card. Despite this, from a user’s perspective, the PayPay Card mini app had a noticeably slow display speed. While often wondering, “Why is it so slow?”, I also felt confident that I could leverage my past experience to improve its speed, which ultimately prompted me to apply.
During the interview, I conveyed my strong passion for speed improvement, and my current manager, who was among the interviewers, responded positively, stating, “We definitely want you to take this on.” With the ambitious goal of the mini app’s top page displaying within 1 second of launch, I began working on speed improvement.
Driving Speed Improvement with Sprints: Achieving Over 30% Acceleration
How did you approach the speed improvement project?
As this was a project assigned to me shortly after joining, I dedicated the first month to onboarding and setting up the development environment. During this period, my manager and other team members consistently arranged icebreakers and informal 1-on-1 sessions, which greatly facilitated smooth relationship building—crucial for development.
Starting the following month, I focused on thoroughly understanding the current situation. As a user, I felt it took 6 to 7 seconds for the mini app to launch and the screen to display, and an additional 2 to 3 seconds for each subsequent operation. However, PayPay Card’s internal perception was that it only took about 1.5 to 2 seconds. Upon analyzing the root cause, we discovered an issue with the speed measurement methodology.
Specifically, measurements were being taken in ideal network environments with all data cached, and manual measurements also exhibited variability. Users often open the mini app outdoors or in environments with poor network quality, and they don’t necessarily launch the mini app every day to acquire cached data. These factors contributed to a significant discrepancy in perceived speed. To address this, we introduced an automated measurement system that replicated conditions closer to the actual user environment and eliminated variations in numerical values caused by different measurers.
Next, our analysis of the slowdown’s causes revealed that downloading static resources and acquiring dynamic resources were taking longer than expected. We also identified areas for improvement in the design components commonly used by product members. Based on our hypotheses, we advocated for the benefits of reducing package size and collaborated with the relevant departments to implement these improvements.
Please tell us about the results of the improvements?
As a result of deleting unnecessary resources, compressing file sizes, and consolidating APIs to convert some transitions into Single-Page Applications (SPAs), we successfully reduced static resources by over 70% in approximately four months, and consolidated more than a dozen APIs into a single one. The size of design components was also compressed by over 60%, and the display time of the top page decreased by 33%. We achieved values close to our target of under 1 second.
However, speed improvement is an ongoing process, and many improvements remain to be completed. We aim to focus on fundamental improvements at the mini app’s architecture level, which may take time but promise significant results. Additionally, we are committed to establishing an environment where highly skilled front-end engineers can lead development.
What was the most challenging aspect of the project?
The most challenging aspect was balancing the desire to implement numerous improvements with the urgency to achieve visible results as quickly as possible. To accomplish improvements within a very short timeframe, I organized the workload and priorities, drawing a clear line between initiatives to undertake and those to defer. Once the initiatives were decided, we utilized sprints to relentlessly iterate through trial and error, gradually releasing improvements.
To proceed quickly, I made a conscious effort to act without hesitation and simply get things done. This involved simultaneously progressing multiple improvements while also conducting reviews to ensure quality. I approached my own tasks with the same parallel processing mindset I applied to the top page speed improvement.
Furthermore, given the need for detailed coordination and knowledge sharing between teams, I focused on understanding the products and cultures of other teams. Although many Japanese members were present, I used speed improvement as a conversation starter to communicate with as many members as possible. The PayPay Card members, transcending nationality and language barriers, fully supported my challenge, enabling me to gain a wealth of knowledge that contributed to speed improvement.
What growth did you experience through this project?
I feel I’ve truly leveled up as an engineer. Previously, I tended to be a “problem-solver,” merely addressing challenges assigned to me by others. However, in this project, by conducting self-verification based on hypotheses and implementing improvements, I truly felt I was moving closer to becoming a “problem-finder” who can contribute to the organization from the initial stage of issue identification.
Finally, do you have a message for our readers?
PayPay Card is a company that genuinely values initiatives like performance improvement, even if they don’t directly lead to short-term revenue. Furthermore, as a rapidly growing company, frequent feature releases are possible, granting you the discretion to take on challenges that enhance user experience. Automation is also advancing, enabling you to focus on your core responsibilities.
I believe that an engineer’s greatest reward lies in discovering challenging problems and experiencing significant personal growth through the process of solving them. If you are an engineer eager to challenge product improvements and experience growth in an environment where your efforts are correctly evaluated and valued, we would love for you to become a colleague at PayPay Card.
*Job openings and employee affiliations are current as of the time of the interview.