Built on the WeChat social platform, WeChat Mini-Programs are widely used by more than 400 million users every day. Consequently, the reliability of Mini-Programs is particularly crucial. However, WeChat Mini-Programs suffer from various bugs related to execution environment, lifecycle management, asynchronous mechanism, etc. These bugs have seriously affected users' experience and caused serious impacts.

In this paper, we conduct the first empirical study on 83 WeChat Mini-Program bugs, and perform an in-depth analysis of their root causes, impacts and fixes. From this study, we obtain many interesting findings that can open up new research directions for combating WeChat Mini-Program bugs. Based on the bug patterns found in our study, we further develop WeDetector to detect WeChat Mini-Program bugs. Our evaluation on 25 real-world Mini-Programs has found 11 previously unknown bugs, and 7 of them have been confirmed by developers.