The Mad Scientist Review - GJS Promise example

gio-cat.js

const GLib = imports.gi.GLib;
const Gio = imports.gi.Gio;

function wrapPromise(obj, cancellable, asyncName, finishName, ...inArgs) {
    return new Promise((resolve, reject) => {
        let callerStack = new Error().stack
            .split('\n')
            .filter(line => !line.match(/<Promise>|wrapPromise/))
            .join('\n');
        obj[asyncName](...inArgs, cancellable, (obj, res) => {
            try {
                let results = obj[finishName](res);
                resolve(results);
            } catch (e) {
                e.stack += '--- Called from: ---\n' + callerStack;
                reject(e);
            }
        });
    });
}
function loadContents(file, cancellable=null) {
    return wrapPromise(file, cancellable, 'load_contents_async',
        'load_contents_finish');
}

// -------------------------

let loop = GLib.MainLoop.new(null, false);

function cat(filename) {
    let f = Gio.File.new_for_commandline_arg(filename);
    loadContents(f)
    .then(([ok, contents]) => {
        print(contents);
    })
    .catch(e => {
        logError(e);
    })
    .then(() => loop.quit());

    loop.run();
}

if (ARGV.length != 1) {
    printerr("Usage: gio-cat.js filename");
} else {
    cat(ARGV[0]);
}