Install

Using NPM:

npm install es6-simple-async

Async

This is a basic wrapper around generators to create async functions:

var async = require('es6-simple-async');

var timer = function(time) {
    return new Promise(function(resolve) {
        setTimeout(resolve, time);
    });
};

var delay = async(function*(time, message) {
    yield timer(time);
    console.log(message);
});

async.main(function*() {
    yield delay(1000, "Hello");
    yield delay(2000, "Goodbye");
});

Functions

async(genFunction)

This function takes a generator function and returns a function that will return a promise. Inside the generator whenever a yield is reached the value will be turned into a Promise then when the Promise is resolved it will resume the generator sending the value to the generator.

var async = require('es6-simple-async');

var timer = function(time) {
    return new Promise(function(resolve) {
        setTimeout(resolve, time);
    });
};

var delay = async(function*(value, time) {
    yield timer(1000); // Asynchrously completes the promise then
                       // resumes the generator at this position
    return value; // Resolves the promise of the async function so any
                  // async function yielding on a Promise returned by this
                  // function will recieve value when it resumes
});

async.main(function*() {
    var value = yield delay('cats', 1000); // recieves value cat after
                                           // 1000 milliseconds
    console.log("Value");
});

Errors are thrown back into the generator so:

var task = async(function*() {
    try {
        var data = yield request('www.google.com');
    } catch (err) {
        // If request('www.google.com') rejects for whatever reason we'll
        // an error will be thrown at the yield statement so we can just
        // wrap it in a try/catch block as usual
        console.log("Couldn't get data");
    };
});

async.run(genFunc) / async.do(genFunc)

async.run (or the async.do alias) immediately invokes the given async function and returns a Promise for the value returned:

var timer = function(time) {
    return new Promise(function(resolve) {
        setTimeout(resolve, time);
    });
};

async.run(function*() {
    yield timer(1000);
    return 3;
}).then(function(value) {
    console.log(value); // Prints 3 after 1000 seconds
});

async.main(genFunc)

async.main is much like async.run but if there's an error it will print it to the console.

async.from(iterable)

async.from converts an iterable into an async function, this could be useful if creating custom iterators instead of using generators.

var async = require('es6-simple-async');

var timer = function(time) {
    return new Promise(function(resolve) {
        setTimeout(resolve, time);
    });
};

var delay = async(function*(value, time) {
    yield timer(1000); // Asynchrously completes the promise then
                       // resumes the generator at this position
    return value; // Resolves the promise of the async function so any
                  // async function yielding on a Promise returned by this
                  // function will recieve value when it resumes
});

var CustomIterator = function() {
    this.value = 0;
};

CustomIterator.prototype.next = function() {
    if (this.value < 10) {
        this.value = this.value + 1;
        var result = delay('cats', 1000);
        return {value: result, done: false};
    } else {
        return {value: 10, done: true};
    };
};

CustomIterator.prototype[Symbol.iterator] = function() {
    return this;
};

var task = async.from(new CustomIterator());
task().then(function(value) {
    console.log(value); // Prints 10 after 10 seconds
});