Lightweight Promise implementation with the "finally" method
Native Promise in ECMAScript 2015 came without "finally" while this method is really useful in many cases.
For an instance, let's start with the following script:
var Article = require('../models/Article');
export var home = (req, res) => {
let query = req.query || {};
let skip = query.skip || 0;
let limit = query.limit || 10;
let data = {
error: 0,
entries: []
};
I don't think that's good to write something like this:
return Article.list(skip, limit).then((result) => {
data.entries = result;
res.render('landing', data);
}).catch((err) => {
data.error = err;
res.render('landing', data);
});
};
However, it's better to have "finally" there:
return Article.list(skip, limit).then((result) => {
data.entries = result;
}).catch((err) => {
data.error = err;
}).finally(() => {
res.render('landing', data);
});
};
Unfortunately, "finally" is only available in some libraries such as Bluebird, or Q+, those are quite heavy to load for client side usage. What I need is just a basic prototype, a simple polyfill with "finally" implemented.
This variant provides the Promise constructor and 4 static methods:
- Promise.resolve
- Promise.reject
- Promise.all
- Promise.series (since v0.0.9)
Promise.series works as same as async.series but follows Promise style, for example:
Promise.series([
(next) => {
setTimeout(next, 300);
},
(next) => {
setTimeout(next, 100);
},
(next) => {
setTimeout(next, 500);
},
(next) => {
setTimeout(next, 2000);
},
(next) => {
setTimeout(next, 1000);
}
]).then(() => {
console.log('Promise.series: then');
}).catch((err) => {
console.log('Promise.series: catch');
console.log(err);
}).finally(() => {
console.log('Promise.series: finally');
});
In node.js
npm install promise-wtf
And then:
var fs = require('fs');
var Promise = require('promise-wtf');
var read = (file) => {
return new Promise((resolve, reject) => {
fs.readFile(file, 'utf8', (err, content) => {
if (err) {
return reject(err);
}
return resolve(content);
});
});
};
read('./hello.txt').then((a) => {
a += 'I like Promise';
return a;
}).then((b) => {
b += '\nI need finally';
return b;
}).then((c) => {
console.log(c);
}).catch((err) => {
console.log(err);
}).finally(() => {
console.log('Done');
});
Ouput:
Hello
I like Promise
I need finally
Done
System.config({
baseURL: '/path/to/promise-wtf.js/folder',
map: {
promise: 'promise-wtf'
}
});
System.import('promise').then(function(Promise){
// use Promise here
});
require.config({
baseUrl: '/path/to/promise-wtf.js/folder',
paths: {
promise: 'promise-wtf'
}
});
requirejs('promise', function(Promise){
// use Promise here
});
git clone https://github.com/ndaidong/promise-wtf.git
cd promise-wtf
npm install
npm test
The MIT License (MIT)