grunt-watch configuration to run with Rails and Jasmine (grunt-contrib-jasmine)

Gruntfile.js

// This file expects the specs to have the same name ending with '.spec.js' and to be in the same folder structure than the source
// Example: 
//  /app/assets/javascripts/models/todo.js
//  /spec/javascripts/models/todo.spec.js

// It runs only the spec of the changed file or, if it's not found, runs the entire suite
module.exports = function(grunt) {
    grunt.initConfig({
        jasmine: {
            all: {
                src: [
                  "http://localhost:3000/assets/application.js"  
                ],
                options: {
                    version: "2.0.0",
                    specs: [
                        "spec/javascripts/**/*.spec.js"
                    ]
                }
            }
        },
        watch: {
            scripts: {
                files: ["app/assets/javascripts/**/*.js", "spec/javascripts/**/*.spec.js"],
                options: {
                    spawn: false,
                }
            }
        }
    });

    grunt.event.on('watch', function(action, changedFilePath) {
        var specsPath = "spec/javascripts/";

        // If the file is a spec run it
        if(changedFilePath.search(".spec.js") > -1) {
            specsPath = changedFilePath;
        } else {
            // Find and run the spec for this particular file, if it exists
            // If it doesn't run all files
            var filepath = specsPath + changedFilePath.split("/javascripts")[1].replace(/\.js$/, ".spec.js");

            if (grunt.file.exists(filepath)) {
                specsPath = filepath;
            } else {
                specsPath += "**/*.spec.js";
            }
        }

        grunt.config("jasmine.all.options.specs", [specsPath]);
        grunt.task.run("jasmine:all");
    });

    grunt.loadNpmTasks("grunt-contrib-jasmine");
    grunt.loadNpmTasks("grunt-contrib-watch");

    grunt.registerTask("default", ["watch"]);
};