My code folders and files are like this, you never know how many sub folders in it:

js/sub1/a.js

js/sub2/b.js

js/sub3/sub31/c.js

js/sub4/sub41/sub411/d.js

Here is part of the Gruntfile.js:

grunt.initConfig({

    watch: {

        src: {

            files: ['js/*.js'],

            tasks: []

        }

    }

});

Grunt can't watch the changes of my all JavaScript files by using 'js/*.js'. So how to write the correct file path expression?