A JavaScript function can be used to build a client. When the build property is a function, truffle will run that function whenever we want to build the client. The function is given a lot of information about the project with which to integrate with truffle.

You can make truffle run a function to build the client using similar configuration code:

module.exports = { 
  build: function(options, callback) { 
     // Do something when a build is required. `options` contains these values: 
     // 
     // working_directory: root location of the project 
     // contracts_directory: root directory of .sol files 
     // destination_directory: directory where truffle expects the built assets (important for `truffle serve`) 
  } 
}