The performance of some map applications can be improved not only through the compression of raster files or appropriate data server configuration, but also by using source file minification. Minification can be more or less effective. The objective of the paper is to perform a comparative analysis of selected online tools for minifying JavaScript code and to measure the impact of such minification on the performance of a map application. Minification and performance tests were conducted on a prototype map application. The application was developed as a ZoomLens component extending the functionality of any website. Various tools yielded similar results of the JavaScript file minification, and it did not affect the values of aggregate performance indices. In most cases, it reduced the JavaScript file size by over a half. It has been demonstrated that minification of JavaScript code alone may not be sufficient to improve the application performance noticeably.