p

yet another A+ Promise (small enough to include in your own library)

Install via npm:

$ npm install ppromise --save

In addition to the specified A+ behavior:

var readJSON = new Promise(function(resolve, reject){
    fs.readFile('something.json', {encoding : 'utf-8'}, function(err, result){
        if (err){
            reject(err);
        } else {
            resolve(JSON.parse(result));
        }
    });
});

readJSON.then(function(data){
    console.log(data.awesome);
}, function(err){
    console.error(err);
})

p also implements Promise.all:

Promise.all([promiseA, promiseB, promiseC]).then(function(results){
    var promiseAResult = results[0];
    var promiseBResult = results[1];
    var promiseCResult = results[2];
});

and the creation of Deferreds when passing no arguments to the constructor:

var dfd = new Promise();
var promise = dfd.promise(); // this will only contain the `then`
fs.readFile('something.json', {encoding : 'utf-8'}, function(err, result){
    if (err){
        dfd.reject(err);
    } else {
        dfd.resolve(JSON.parse(result));
    }
});
dfd.then(function(data){
    console.log(data.awesome);
}, function(err){
    console.error(err);
})

The library works as AMD or CommonJS module, or as a plain script tag (exporting to window.Promise). If you'd like to get back the original window.Promise (i.e. native implementations) you can use Promise.noConflict:

var pPromise = Promise.noConflict();
console.log(Promise) // => function(){ [native code] } (or undefined)

License

MIT © Frederik Ring