closure

Make Sure you donwnloaded Google Closure Compiler

For the purpose of this example , extract the downloaded archive and rename to compiler.jar

You can minify your js file by using google closure compiler

java -jar compiler.jar --js app.js --js_output_file app.min.js

You can also run it ith advanced optimization by running this command

java -jar compiler.jar --js app.js --js_output_file app.min.js --compilation_level ADVANCED_OPTIMIZATIONS

or you can use optimization level White space only

java -jar compiler.jar --js app.js --js_output_file app.min.js --compilation_level WHITE_SPACE_ONLY

sometime we may need to see the warnings even if we made optimization

java -jar compiler.jar --js app.js --js_output_file app.min.js --compilation_level ADVANCED_OPTIMIZATIONS --warning_level VERBOSE

In case of JQuery for example you may encounter an error $ is undeclared

so you may want to use --externs option for that and before using it you need to go to their jquery closure library and download the file and put it in your project and run this command with --externs option

java -jar compiler.jar --js app.js --js_output_file app.min.js --compilation_level ADVANCED_OPTIMIZATIONS --warning_level VERBOSE --externs jquery.closure.js

If you are using console.log in your code you'd definitely have an error , because the default is when the compiler founds a non declared variable it throw the error , so you may use this option to ignore this kind of error

java -jar compiler.jar --js app.js --js_output_file app.min.js --compilation_level ADVANCED_OPTIMIZATIONS --warning_level VERBOSE --externs jquery.closure.js --jscomp_off=checkVars