index.js

#!/usr/bin/env node

const pkg = require('./package.json');
const updateNotifier = require('update-notifier')({pkg});
if(updateNotifier.update){
    updateNotifier.notify({defer:false}); // display plz-update notification message
    setTimeout(main, 5000); // start after 5 seconds
}else{
    main(); // up to date - start right away
}

function main(){
    console.log("v" + pkg.version + " - coded Nov17 by Lars Froelich\n");
    console.log("*** Merge-PDFs ***");
    const cwd = process.cwd();

    // configure program-parameters
    var program = require('commander')
        .option('-e, --even', 'Add empty pages to PDFs that end on odd pages (useful for manual duplex printing)')
        .parse(process.argv);

    console.log("  - loading dependencies");
    const pdfjs = require('pdfjs');
    const fs = require("fs");
    const readdir = require("recursive-readdir");

    console.log("  - loading font");
    var helvetica = fs.readFileSync(__dirname + '/Helvetica.json');
    helvetica = JSON.parse(helvetica);
    var helveticaf = new pdfjs.Font(helvetica);

    console.log("  - creating output pdf");
    var doc = new pdfjs.Document({font: helveticaf});

    var totalCount = 0;
    var evenCount = 0;
    console.log("  - adding PDFs");
    readdir(cwd, ["!*.pdf", "merged.pdf"]).then( // get all pdf-files except previous merges
        function(pdfs) {
            pdfs.forEach(function(pdf){
                console.log("  + adding \"" + pdf.replace(/^.*[\\\/]/, '') + "\"  (" + pdf + ")");
                var file = fs.readFileSync(pdf);
                var ext =  new pdfjs.ExternalDocument(file);
                doc.addPagesOf(ext);
                totalCount += ext.pageCount;
                if(program.even && (ext.pageCount % 2 === 1)){
                    doc.text(' . '); // some printers don't "skip" this page if it's entirely empty.
                    totalCount ++;
                    evenCount ++;
                }
            });
            console.log("  - writing output-file");
            doc.pipe(fs.createWriteStream(cwd + '/merged.pdf'));
            doc.end().then(function () {
                console.log("\n Finished writing PDF (" + totalCount + " pages total).\n Merged output is 'merged.pdf'");
                if(program.even){
                    console.log(" " + evenCount + " empty pages have been added to PDFs with odd numbers of pages.");
                }
            });
        },
        function(error) {
            console.error("Unable to search for pdf-files ", error);
        }
    );
}