71 lines
2.4 KiB
JavaScript
71 lines
2.4 KiB
JavaScript
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"use strict";
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Object.defineProperty(exports, "__esModule", {
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value: true
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});
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exports.default = void 0;
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var _errors = require("./errors");
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// Like an EventEmitter, but for only a single "event". This provides type-safety
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// for the values emitted. Rather than passing predetermined strings (which can
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// be misspelled), create an instance of ValueEmitter for every logical "event"
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// to be dispatched, and type it according to the type of value emitted.
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class ValueEmitter {
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// An array of listeners. One might think a Set would be better for O(1) removal,
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// but splicing a JS array gets pretty close, and copying the array (as is done
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// in emit) is far faster than a Set copy: https://github.com/atom/event-kit/pull/39
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_listeners = [];
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_disposed = false;
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addListener(listener) {
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if (this._disposed) {
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throw new _errors.AlreadyDisposedError('Cannot add a listener since this ValueEmitter has been disposed');
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}
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this._listeners.push(listener);
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// Close over a reference to this emitter in the disposable below, rather
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// than referencing `this` directly. This allows us to set it to null after
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// slicing out the listener.
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// This prevents anyone holding onto the disposable after disposal from
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// unintentionally retaining a reference to this emitter.
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let emitter = this;
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return {
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dispose() {
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if (emitter == null) {
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return;
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}
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if (emitter._disposed) {
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emitter = null;
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return;
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}
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let listeners = emitter._listeners;
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let listenerIndex = listeners.indexOf(listener);
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if (listenerIndex > -1) {
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listeners.splice(listenerIndex, 1);
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}
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emitter = null;
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}
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};
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}
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emit(value) {
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if (this._disposed) {
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throw new _errors.AlreadyDisposedError('Cannot emit since this ValueEmitter has been disposed');
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}
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// Iterate over a copy of listeners. This prevents the following cases:
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// * When a listener callback can itself register a new listener and be
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// emitted as part of this iteration.
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// * When a listener callback disposes of this emitter mid-emit, preventing
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// other listeners from receiving the event.
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let listeners = this._listeners.slice();
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for (let i = 0; i < listeners.length; i++) {
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listeners[i](value);
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}
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}
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dispose() {
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if (this._disposed) {
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return;
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}
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this._listeners = [];
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this._disposed = true;
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}
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}
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exports.default = ValueEmitter;
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