keyvan-m-sadeghi

const states = {
    pending: 'Pending',
    resolved: 'Resolved',
    rejected: 'Rejected'
};

class Nancy {
    constructor(executor) {
        const tryCall = callback => Nancy.try(() => callback(this.value));
        const laterCalls = [];

keyvan-m-sadeghi

class Nancy {
    constructor(executor) {
        ...
        const laterCalls = [];
        const callLater = getMember => callback => new Nancy(resolve => laterCalls.push(() => resolve(getMember()(callback))));
        const members = {
            ...
            [states.pending]: {
                ...
                then: callLater(() => this.then),

keyvan-m-sadeghi

let p = delay(500);
p.then(() => console.log('1st then!')); // after 0.5 seconds, logs 1st then!
p.then(() => console.log('2nd then!')); // after 0.5 seconds, logs 2nd then!
p.then(() => console.log('3rd then!')); // after 0.5 seconds, logs 3rd then!

p = p.then(() => Nancy.reject());
p.catch(() => console.log('1st catch!')); // after 0.5 seconds, logs 1st catch!
p.catch(() => console.log('2nd catch!')); // after 0.5 seconds, logs 2nd catch!
p.catch(() => console.log('3rd catch!')); // after 0.5 seconds, logs 3rd catch!

keyvan-m-sadeghi

const delay = milliseconds => new Nancy(resolve => setTimeout(resolve, milliseconds));
const logThenDelay = milliseconds => total => {
    console.log(`${total / 1000.0} seconds!`);
    return delay(milliseconds)
        .then(() => total + milliseconds);
};

logThenDelay(500)(0) // logs 0 seconds!
    .then(logThenDelay(500)) // after 0.5 seconds, logs 0.5 seconds!
    .then(logThenDelay(500)) // after 1 second, logs 1 seconds!

keyvan-m-sadeghi

const apply = (value, state) => {
    // Ignore subsequent calls to resolve and reject
    if (this.state === states.pending) {
        this.value = value;
        changeState(state);
    }
};

const getCallback = state => value => {
    // Unpack on resolve

keyvan-m-sadeghi

let p = new Nancy((resolve, reject) => {
    resolve(42);
    reject(24); // ignored
    resolve(); // ignored
});

p
    .then(value => Nancy.reject(value)) // rejects
    .catch(value => console.log(value)); // logs 42

keyvan-m-sadeghi

const anything = () => {
    throw new Error('I can be anything because I should never get called!');
};
const throwSomethingWrong = () => {
    console.log('not ignored!');
    throw new Error('Something went wrong...');
};

const p = Nancy.reject(42)
    .catch(value => value) // resolves

keyvan-m-sadeghi

[states.resolved]: {
    ...
    then: tryCall,
    catch: _ => this
},
[states.rejected]: {
    ...
    then: _ => this,
    catch: tryCall
}

keyvan-m-sadeghi

class Nancy {
    constructor(executor) {
        const tryCall = callback => Nancy.try(() => callback(this.value));
        const members = {
            [states.resolved]: {
                ...
                then: trycall
            },
            ...
        };

keyvan-m-sadeghi

class Nancy {
    constructor(executor) {
        const members = {
            [states.resolved]: {
                state: states.resolved,
                // Chain mechanism
                then: onResolved => Nancy.resolve(onResolved(this.value))
            },
            [states.rejected]: {
                state: states.rejected,