Promise thenable All In One

Promise thenable 是指一个函数或一个对象的里面定义了一个 then 方法

Promises/A+

https://github.com/then/thenable/blob/master/index.js



// Wrapped

function Wrapped(thenable) {

  this.val = thenable;

}

Wrapped.prototype.unwrap = function () {

  return this.val;

};

// wrap

function wrap(thenable) {

  return new Wrapped(thenable);

}

// unwrap

function unwrap(wrapped) {

  return wrapped instanceof Wrapped ? wrapped.unwrap() : wrapped;

}

exports.wrap = wrap;

exports.unwrap = unwrap;

ECMA 262

https://tc39.es/ecma262/#sec-newpromiseresolvethenablejob

MDN

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/resolve

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/then

refs

https://javascript.info/promise-chaining



class Thenable {

  constructor(num) {

    this.num = num;

  }

  then(resolve, reject) {

    alert(resolve); // function() { native code }

    // resolve with this.num*2 after the 1 second

    setTimeout(() => resolve(this.num * 2), 1000); // (**)

  }

}

new Promise(resolve => resolve(1))

  .then(result => {

    return new Thenable(result); // (*)

  })

  .then(alert); // shows 2 after 1000ms

https://masteringjs.io/tutorials/fundamentals/thenable

https://exploringjs.com/es6/ch_promises.html#sec_chaining-promises

https://medium.com/javascript-in-plain-english/whats-the-difference-between-a-thenable-and-a-promise-74d697bc9c79

https://stackoverflow.com/questions/53894038/whats-the-difference-between-resolvethenable-and-resolvenon-thenable-object