createAppCache.js

let fs = require('fs');
let glob = require('glob');

let getFiles = (filter) => {
    return new Promise(resolve => {
        glob(filter, (err, innerfiles) => {
            resolve(innerfiles);
        });
    });
}

let getAllFiles = (filters) => {
    var promises = [];
    for (var i = 0; i < filters.length; i++) {
        var promise = getFiles(filters[i]);
        promises.push(promise);
    }

    return Promise.all(promises).then(fileArrays => {
        var allFiles = [];

        for (var j = 0; j < fileArrays.length; j++) {
            var fileArray = fileArrays[j];
            allFiles = allFiles.concat(fileArray);
        }

        return allFiles;
    });
}

let writeFile = (fileName, content) => {
    return new Promise(resolve => {
        fs.writeFile(fileName, content, 'utf8', function (err) {
            if (err) return console.log(err);
            resolve();
        });
    });
}

getAllFiles([ "./app/*.js", "./app/*.html", "./app/*.ico", "./app/*.css", "./app/*.txt" ]).then(files => {
    var content = `CACHE MANIFEST

CACHE:
`;
    for (var k = 0; k < files.length; k++) {
        var fileName = files[k];
        content += fileName.replace("./app/", "") + `
`;
    }

    content += `
NETWORK:
*`;

    writeFile("./app/cache.manifest", content);
});