73 lines
1.7 KiB
JavaScript
73 lines
1.7 KiB
JavaScript
(function(factory) {
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if (typeof define !== 'undefined' && define.amd) {
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define([], factory);
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} else if (typeof define !== 'undefined' && define.petal) {
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define(['promise-stream'], [], factory);
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} else if (typeof module !== 'undefined' && module.exports) {
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module.exports = factory();
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} else {
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window.PromiseStream = factory();
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}
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})(function() {
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class PromiseStream {
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constructor() {
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this._current = new Promise((resolve) => {
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this._resolve = resolve;
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});
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this._next = this._current;
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this._value = undefined;
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}
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get promise() {
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/* waits for the _first_ update, or completes immediately */
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return this._current;
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}
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get next_promise() {
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/* waits for the _next_ update (which may be the first) */
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return this._next;
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}
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get value() {
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return this._value;
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}
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update(value) {
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if (value !== undefined && value !== this._value) {
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const resolve = this._resolve;
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const current = this._next;
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const next = new Promise((resolve) => {
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this._resolve = resolve;
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});
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this._current = current;
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this._next = next;
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this._value = value;
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resolve({ value, next });
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}
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}
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once(cb) {
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this.promise.then((v) => { cb(v.value); });
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}
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listen(cb) {
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let cancelled = false;
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function renew(v) {
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if (!cancelled) {
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cb(v.value);
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v.next.then(renew);
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}
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}
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this.promise.then(renew);
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return () => { cancelled = true; };
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}
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}
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return PromiseStream;
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});
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