A Java developer we have the good habits to split the building process of a project in steps.
2. Concatenation: when an application is distributed is easier to manage only one file than dozens. The concatenation is used to merge multiple files in only one. This is similar to the concept of FatJar in Java.
3. Minification: the code file used in a JS project contains many useless characters (for the interpreter). The minification process try to optimize the code reducing the size of the JS file. In Java is the compile that optimize the code.
In Java the common used tools for the building process are : maven, gradle and ant