Physlets are a widely used teaching resource developed at Davidson College consisting of scriptable Java applets designed to simulate a wide variety of physical phenomena.  Within the last few years, all major browsers have removed the plug-in that enabled Java applets on web pages, thereby breaking all web sites that utilize the original Java Physlet applets.  This is a major setback for physics education, since there are thousands of Physlet-based html pages in use worldwide.  This paper reports the successful conversion of Physlets to JavaScript, allowing Physlet-based curricular material to be used again on all computer platforms, including mobile devices.  The code conversion technology, applicable to most Java applets and applications, allows developers to continue developing in Java with minimal recoding and concurrent real-time automated production of both Java and JavaScript versions.  The Third Edition of Physlet Physics, available at no cost on the AAPT-ComPADRE digital library, shows how the Java to JavaScript conversion works in practice.