| jpt | JProbe Threadalyzer Memory Snapshot |
| jpy | JPY Data |
| jr | JR Source Code |
| jrag | JastAdd Declarative Aspect |
| jrprint | JasperReports Print Document |
| jrxml | JasperReports Document |
| js | JavaScript |
| js | JavaScript Style Sheet |
| jsa | JRun Server Application |
| jsb | JAWS Script Binary File |
| jsb | JavaScript Bean |
| jsc | Rhino Compiled Javascript |
| jsc | Jeroo Source Code |
| jscript | Windows Media Player JScript |
| jsd | JAWS Script Documentation File |
| jsdtscope | Eclipse IDE JavaScript Development Tool Scope Data |
| jsfl | Flash JavaScript |
| jsh | Jsh Script |
| jsh | JAWS Script Header |
| jsi | JAWS Personal Settings Data |
| jsl | JMP Scripting Language File |
| jslib | Unity WebGL Extension |
| jsm | JavaScript Module |
| jsm | JAWS Script Message File |
| jsp | Java Servlet |
| jspa | Java Servlet Alias |
| jspf | Java Server Page Fragment |
| jspre | Unity WebGL Extension |
| jspx | Java Servlet XML |
| jss | JAWS Script Source |
| jss | JavaScript Style Sheet |
| jst | Code Crusader Symbol Database |
| jsx | Adobe ExtendScript File |
| jsxbin | Adobe ExtendScript Binary File |
| jsxinc | Adobe ExtendScript Include File |