gulpfile-sw-precache.js

elixir(function(mix) {
    // My elixir code goes here
});

gulp.task('generate-service-worker', function(callback) {
    var swPrecache = require('sw-precache');
    var rootDir = 'public';

    swPrecache.write(`${rootDir}/service-worker.js`, {
        staticFileGlobs: [
            rootDir + '/build/**/*.{js,css}',
            rootDir + '/img/**/*.{jpg,png,svg}'
        ],
        stripPrefix: rootDir
    }, callback);
});