gruntjs - Change the configuration of the task uglify dynamically -

i need change configuration of uglify task minify file needed (as explained here jshint task : https://github.com/gruntjs/grunt-contrib-watch#compiling-files-as-needed)

the modification works jshint task not uglify, think problem property path...

any appreciated ;)

here gruntfile.js :

module.exports = function (grunt) {     grunt.initconfig({          // define source files , destinations         jshint: {             all: ['dev/**/*.js'],         },         uglify: {             dynamic_mappings: {               // grunt search "**/*.js" under "dev/" when "minify" task               // runs , build appropriate src-dest file mappings then,               // don't need update gruntfile when files added or removed.             files: [{                   expand: true,     // enable dynamic expansion.                   cwd: 'dev/',      // src matches relative path.                   src: ['**/*.js'], // actual pattern(s) match.                   dest: 'build',   // destination path prefix.                   ext: '.min.js',   // dest filepaths have extension.                 },               ],             }         }         watch: {         options: { spawn: false },             js:  { files: 'dev/**/*.js', tasks: [ 'uglify' ] },         }     });      // load plugins     grunt.loadnpmtasks('grunt-contrib-watch');     grunt.loadnpmtasks('grunt-contrib-uglify');     grunt.loadnpmtasks('grunt-contrib-jshint');      // default task     grunt.registertask('default', [ 'watch' ]);      grunt.event.on('watch', function(action, filepath) {         grunt.config(['jshint', 'all'], filepath);         grunt.config('uglify.dynamic_mappings.files', [{src: filepath }]);     });  }; 

the line

grunt.config('uglify.dynamic_mappings.files', [{src: filepath }]); 

is replacing original configuration uglify.dynamic_mappings.files

instead try including other original parameters along new src: filepath