tricks
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ES6 modules
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JavaScript
// Then
// Create a Promise instance which can be returned by a function
import setImmediate from '../time/setImmediate.js';
/* !
** Thenable -- Embeddable Minimum Strictly-Compliant Promises/A+ 1.1.1 Thenable
** Copyright (c) 2013-2014 Ralf S. Engelschall <http://engelschall.com>
** Licensed under The MIT License <http://opensource.org/licenses/MIT>
** Source-Code distributed on <http://github.com/rse/thenable>
*/
/* promise states [Promises/A+ 2.1] */
const STATE_PENDING = 0; /* [Promises/A+ 2.1.1] */
const STATE_FULFILLED = 1; /* [Promises/A+ 2.1.2] */
const STATE_REJECTED = 2; /* [Promises/A+ 2.1.3] */
function api(executor) {
/* optionally support non-constructor/plain-function call */
if (!(this instanceof api))
return new api(executor);
/* initialize object */
this.id = 'Thenable/1.0.6';
this.state = STATE_PENDING; /* initial state */
this.fulfillValue = undefined; /* initial value */ /* [Promises/A+ 1.3, 2.1.2.2] */
this.rejectReason = undefined; /* initial reason */ /* [Promises/A+ 1.5, 2.1.3.2] */
this.onFulfilled = []; /* initial handlers */
this.onRejected = []; /* initial handlers */
/* provide optional information-hiding proxy */
this.proxy = {
then: this.then.bind(this)
};
/* support optional executor function */
if (typeof executor === 'function')
executor.call(this, this.fulfill.bind(this), this.reject.bind(this));
}
/* execute particular set of handlers */
const execute_handlers = function(curr, name, value) {
/* short-circuit processing */
if (curr[name].length === 0)
return;
/* iterate over all handlers, exactly once */
const handlers = curr[name];
curr[name] = []; /* [Promises/A+ 2.2.2.3, 2.2.3.3] */
setImmediate(() => {
for (let i = 0; i < handlers.length; i++)
handlers[i](value); /* [Promises/A+ 2.2.5] */
});
};
/* execute all handlers */
const execute = function(curr) {
if (curr.state === STATE_FULFILLED)
execute_handlers(curr, 'onFulfilled', curr.fulfillValue);
else if (curr.state === STATE_REJECTED)
execute_handlers(curr, 'onRejected', curr.rejectReason);
};
/* deliver an action */
const deliver = function(curr, state, name, value) {
if (curr.state === STATE_PENDING) {
curr.state = state; /* [Promises/A+ 2.1.2.1, 2.1.3.1] */
curr[name] = value; /* [Promises/A+ 2.1.2.2, 2.1.3.2] */
execute(curr);
}
return curr;
};
/* 'Promise Resolution Procedure' */ /* [Promises/A+ 2.3] */
const resolve = function(promise, x) {
/* sanity check arguments */ /* [Promises/A+ 2.3.1] */
if (promise === x || promise.proxy === x) {
promise.reject(new TypeError('cannot resolve promise with itself'));
return;
}
/* surgically check for a 'then' method
(mainly to just call the 'getter' of 'then' only once) */
let then;
if ((typeof x === 'object' && x !== null) || typeof x === 'function') {
try {
then = x.then;
} /* [Promises/A+ 2.3.3.1, 3.5] */
catch (e) {
promise.reject(e); /* [Promises/A+ 2.3.3.2] */
return;
}
}
/* handle own Thenables [Promises/A+ 2.3.2]
and similar 'thenables' [Promises/A+ 2.3.3] */
if (typeof then === 'function') {
let resolved = false;
try {
/* call retrieved 'then' method */ /* [Promises/A+ 2.3.3.3] */
then.call(x,
/* resolvePromise */ /* [Promises/A+ 2.3.3.3.1] */
y => {
if (resolved) return; resolved = true; /* [Promises/A+ 2.3.3.3.3] */
if (y === x) /* [Promises/A+ 3.6] */
promise.reject(new TypeError('circular thenable chain'));
else
resolve(promise, y);
},
/* rejectPromise */ /* [Promises/A+ 2.3.3.3.2] */
r => {
if (resolved) return; resolved = true; /* [Promises/A+ 2.3.3.3.3] */
promise.reject(r);
}
);
}
catch (e) {
if (!resolved) /* [Promises/A+ 2.3.3.3.3] */
promise.reject(e); /* [Promises/A+ 2.3.3.3.4] */
}
return;
}
/* handle other values */
promise.fulfill(x); /* [Promises/A+ 2.3.4, 2.3.3.4] */
};
/* generate a resolver function */
const resolver = function(cb, next, method) {
return function(value) {
if (typeof cb !== 'function') /* [Promises/A+ 2.2.1, 2.2.7.3, 2.2.7.4] */
next[method](value); /* [Promises/A+ 2.2.7.3, 2.2.7.4] */
else {
let result;
try {
result = cb(value);
} /* [Promises/A+ 2.2.2.1, 2.2.3.1, 2.2.5, 3.2] */
catch (e) {
next.reject(e); /* [Promises/A+ 2.2.7.2] */
return;
}
resolve(next, result); /* [Promises/A+ 2.2.7.1] */
}
};
};
/* promise API methods */
api.prototype = {
/* promise resolving methods */
fulfill(value) {
return deliver(this, STATE_FULFILLED, 'fulfillValue', value);
},
reject(value) {
return deliver(this, STATE_REJECTED, 'rejectReason', value);
},
/* 'The then Method' [Promises/A+ 1.1, 1.2, 2.2] */
then(onFulfilled, onRejected) {
const curr = this;
const next = new api(); /* [Promises/A+ 2.2.7] */
curr.onFulfilled.push(
resolver(onFulfilled, next, 'fulfill')); /* [Promises/A+ 2.2.2/2.2.6] */
curr.onRejected.push(
resolver(onRejected, next, 'reject')); /* [Promises/A+ 2.2.3/2.2.6] */
execute(curr);
return next.proxy; /* [Promises/A+ 2.2.7, 3.3] */
}
};
/* promise object constructor */
export default api;