then.js
903 Bytes
import { config } from './config';
import instrument from './instrument';
import {
noop,
subscribe,
FULFILLED,
REJECTED,
PENDING,
invokeCallback
} from './-internal';
export default function then(onFulfillment, onRejection, label) {
let parent = this;
let state = parent._state;
if (state === FULFILLED && !onFulfillment || state === REJECTED && !onRejection) {
config.instrument && instrument('chained', parent, parent);
return parent;
}
parent._onError = null;
let child = new parent.constructor(noop, label);
let result = parent._result;
config.instrument && instrument('chained', parent, child);
if (state === PENDING) {
subscribe(parent, child, onFulfillment, onRejection);
} else {
let callback = state === FULFILLED ? onFulfillment : onRejection;
config.async(() => invokeCallback(state, child, callback, result));
}
return child;
}