appcache versioning

appcacheTimestampComment.js

// appcacheTimestampComment.js

// script for appcache versioning

// appcache needs an update to the manifest file to allow the browser to check for updated content.
// see [Application Cache is a Douchebag](http://alistapart.com/article/application-cache-is-a-douchebag)

// This script adds a build timestamp to a file that looks like this
//
// # built: Mon Oct 26 2015 10:42:24 GMT+0100 (CET)

// If the last of the file already starts with '# built', it replaces that line with a new timestamp

// overview:
// - read the manifest file
// - check buffer for existing timestamp comment, delete if necessary
// - write back file, add new timestamp comment


var fs = require('fs');

// define path and file to our manifest
var manifestFile = './test.txt';


// first of all, we read the content of the file in question
fs.readFile(manifestFile,'utf8', function read(err, data) {
    if (err) {
        throw err;
    }

    // we want to work with lines – for example count them and find the last line of the file.
    // for that we need to convert the returned data into an array so we can count the lines. we're splitting the string at newline characters (\n).
    var data_array = data.split('\n');

    // we find the last line of the array by subtracting 1 from the array length (because arrays are indexed from 0):
    // data_array[data_array.length - 1]

    // if the last line starts with "# built", there already is a timestamp comment. this needs to be deleted, because we add a new and updated timestamp later
    if ( (data_array[data_array.length - 1]).substring(0, 7)  === '# built' ) {
      console.log('\nthe last line of ' + manifestFile + ' seems to be a comment with the build timestamp, will update that...\n');
      delete data_array[data_array.length - 1];
    } else {
      // if the last line does NOT match the built stamp pattern, leave original content as it is
      // still, we want to tell the user what we found out and tell them that their file will be updated
      console.log('\nthe last line of ' + manifestFile + ' does not seem to be a comment with a build timestamp, will add that...\n');
    }


    // now we need to write back the updated file contents.
    // we first write the file as empty...
    fs.writeFile(manifestFile, '', 'utf8', function (err) {
      if (err) throw err;
      });
      // ...and then append each line from the array plus a line break (\n)
      data_array.forEach(function (line) {
        fs.appendFile(manifestFile, line.toString() + "\n");
      });
      // finally, append the timestamp to the file
      fs.appendFile(manifestFile, '# built: ' + Date());


});


// sources:

// [Application Cache is a Douchebag · An A List Apart Article](http://alistapart.com/article/application-cache-is-a-douchebag)

// [File System Node.js v4.2.1 Manual & Documentation](https://nodejs.org/api/fs.html)

// [javascript - Find String in a Txt File, Delete Entire Line - Stack Overflow](http://stackoverflow.com/questions/22858206/find-string-in-a-txt-file-delete-entire-line/22858388#22858388)

// [javascript - Node.js read and write file lines - Stack Overflow](http://stackoverflow.com/questions/11986350/node-js-read-and-write-file-lines)

// [String.prototype.substring() - JavaScript | MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/substring)

// [Comparison operators - JavaScript | MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Comparison_Operators)