241 lines
11 KiB
JavaScript
241 lines
11 KiB
JavaScript
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import { Observable } from '../Observable';
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import { tryCatch } from '../util/tryCatch';
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import { errorObject } from '../util/errorObject';
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import { AsyncSubject } from '../AsyncSubject';
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/**
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* We need this JSDoc comment for affecting ESDoc.
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* @extends {Ignored}
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* @hide true
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*/
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export class BoundNodeCallbackObservable extends Observable {
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constructor(callbackFunc, selector, args, context, scheduler) {
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super();
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this.callbackFunc = callbackFunc;
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this.selector = selector;
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this.args = args;
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this.context = context;
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this.scheduler = scheduler;
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}
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/* tslint:enable:max-line-length */
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/**
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* Converts a Node.js-style callback API to a function that returns an
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* Observable.
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*
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* <span class="informal">It's just like {@link bindCallback}, but the
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* callback is expected to be of type `callback(error, result)`.</span>
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*
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* `bindNodeCallback` is not an operator because its input and output are not
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* Observables. The input is a function `func` with some parameters, but the
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* last parameter must be a callback function that `func` calls when it is
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* done. The callback function is expected to follow Node.js conventions,
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* where the first argument to the callback is an error object, signaling
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* whether call was successful. If that object is passed to callback, it means
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* something went wrong.
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*
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* The output of `bindNodeCallback` is a function that takes the same
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* parameters as `func`, except the last one (the callback). When the output
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* function is called with arguments, it will return an Observable.
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* If `func` calls its callback with error parameter present, Observable will
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* error with that value as well. If error parameter is not passed, Observable will emit
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* second parameter. If there are more parameters (third and so on),
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* Observable will emit an array with all arguments, except first error argument.
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*
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* Optionally `bindNodeCallback` accepts selector function, which allows you to
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* make resulting Observable emit value computed by selector, instead of regular
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* callback arguments. It works similarly to {@link bindCallback} selector, but
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* Node.js-style error argument will never be passed to that function.
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*
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* Note that `func` will not be called at the same time output function is,
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* but rather whenever resulting Observable is subscribed. By default call to
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* `func` will happen synchronously after subscription, but that can be changed
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* with proper {@link Scheduler} provided as optional third parameter. Scheduler
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* can also control when values from callback will be emitted by Observable.
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* To find out more, check out documentation for {@link bindCallback}, where
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* Scheduler works exactly the same.
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*
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* As in {@link bindCallback}, context (`this` property) of input function will be set to context
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* of returned function, when it is called.
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*
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* After Observable emits value, it will complete immediately. This means
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* even if `func` calls callback again, values from second and consecutive
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* calls will never appear on the stream. If you need to handle functions
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* that call callbacks multiple times, check out {@link fromEvent} or
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* {@link fromEventPattern} instead.
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*
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* Note that `bindNodeCallback` can be used in non-Node.js environments as well.
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* "Node.js-style" callbacks are just a convention, so if you write for
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* browsers or any other environment and API you use implements that callback style,
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* `bindNodeCallback` can be safely used on that API functions as well.
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*
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* Remember that Error object passed to callback does not have to be an instance
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* of JavaScript built-in `Error` object. In fact, it does not even have to an object.
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* Error parameter of callback function is interpreted as "present", when value
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* of that parameter is truthy. It could be, for example, non-zero number, non-empty
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* string or boolean `true`. In all of these cases resulting Observable would error
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* with that value. This means usually regular style callbacks will fail very often when
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* `bindNodeCallback` is used. If your Observable errors much more often then you
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* would expect, check if callback really is called in Node.js-style and, if not,
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* switch to {@link bindCallback} instead.
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*
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* Note that even if error parameter is technically present in callback, but its value
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* is falsy, it still won't appear in array emitted by Observable or in selector function.
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*
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*
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* @example <caption>Read a file from the filesystem and get the data as an Observable</caption>
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* import * as fs from 'fs';
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* var readFileAsObservable = Rx.Observable.bindNodeCallback(fs.readFile);
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* var result = readFileAsObservable('./roadNames.txt', 'utf8');
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* result.subscribe(x => console.log(x), e => console.error(e));
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*
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*
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* @example <caption>Use on function calling callback with multiple arguments</caption>
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* someFunction((err, a, b) => {
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* console.log(err); // null
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* console.log(a); // 5
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* console.log(b); // "some string"
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* });
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* var boundSomeFunction = Rx.Observable.bindNodeCallback(someFunction);
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* boundSomeFunction()
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* .subscribe(value => {
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* console.log(value); // [5, "some string"]
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* });
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*
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*
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* @example <caption>Use with selector function</caption>
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* someFunction((err, a, b) => {
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* console.log(err); // undefined
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* console.log(a); // "abc"
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* console.log(b); // "DEF"
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* });
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* var boundSomeFunction = Rx.Observable.bindNodeCallback(someFunction, (a, b) => a + b);
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* boundSomeFunction()
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* .subscribe(value => {
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* console.log(value); // "abcDEF"
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* });
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*
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*
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* @example <caption>Use on function calling callback in regular style</caption>
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* someFunction(a => {
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* console.log(a); // 5
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* });
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* var boundSomeFunction = Rx.Observable.bindNodeCallback(someFunction);
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* boundSomeFunction()
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* .subscribe(
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* value => {} // never gets called
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* err => console.log(err) // 5
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*);
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*
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*
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* @see {@link bindCallback}
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* @see {@link from}
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* @see {@link fromPromise}
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*
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* @param {function} func Function with a Node.js-style callback as the last parameter.
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* @param {function} [selector] A function which takes the arguments from the
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* callback and maps those to a value to emit on the output Observable.
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* @param {Scheduler} [scheduler] The scheduler on which to schedule the
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* callbacks.
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* @return {function(...params: *): Observable} A function which returns the
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* Observable that delivers the same values the Node.js callback would
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* deliver.
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* @static true
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* @name bindNodeCallback
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* @owner Observable
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*/
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static create(func, selector = undefined, scheduler) {
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return function (...args) {
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return new BoundNodeCallbackObservable(func, selector, args, this, scheduler);
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};
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}
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/** @deprecated internal use only */ _subscribe(subscriber) {
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const callbackFunc = this.callbackFunc;
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const args = this.args;
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const scheduler = this.scheduler;
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let subject = this.subject;
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if (!scheduler) {
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if (!subject) {
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subject = this.subject = new AsyncSubject();
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const handler = function handlerFn(...innerArgs) {
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const source = handlerFn.source;
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const { selector, subject } = source;
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const err = innerArgs.shift();
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if (err) {
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subject.error(err);
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}
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else if (selector) {
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const result = tryCatch(selector).apply(this, innerArgs);
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if (result === errorObject) {
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subject.error(errorObject.e);
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}
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else {
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subject.next(result);
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subject.complete();
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}
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}
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else {
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subject.next(innerArgs.length <= 1 ? innerArgs[0] : innerArgs);
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subject.complete();
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}
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};
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// use named function instance to avoid closure.
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handler.source = this;
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const result = tryCatch(callbackFunc).apply(this.context, args.concat(handler));
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if (result === errorObject) {
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subject.error(errorObject.e);
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}
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}
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return subject.subscribe(subscriber);
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}
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else {
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return scheduler.schedule(dispatch, 0, { source: this, subscriber, context: this.context });
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}
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}
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}
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function dispatch(state) {
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const self = this;
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const { source, subscriber, context } = state;
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// XXX: cast to `any` to access to the private field in `source`.
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const { callbackFunc, args, scheduler } = source;
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let subject = source.subject;
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if (!subject) {
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subject = source.subject = new AsyncSubject();
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const handler = function handlerFn(...innerArgs) {
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const source = handlerFn.source;
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const { selector, subject } = source;
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const err = innerArgs.shift();
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if (err) {
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self.add(scheduler.schedule(dispatchError, 0, { err, subject }));
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}
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else if (selector) {
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const result = tryCatch(selector).apply(this, innerArgs);
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if (result === errorObject) {
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self.add(scheduler.schedule(dispatchError, 0, { err: errorObject.e, subject }));
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}
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else {
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self.add(scheduler.schedule(dispatchNext, 0, { value: result, subject }));
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}
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}
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else {
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const value = innerArgs.length <= 1 ? innerArgs[0] : innerArgs;
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self.add(scheduler.schedule(dispatchNext, 0, { value, subject }));
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}
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};
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// use named function to pass values in without closure
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handler.source = source;
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const result = tryCatch(callbackFunc).apply(context, args.concat(handler));
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if (result === errorObject) {
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self.add(scheduler.schedule(dispatchError, 0, { err: errorObject.e, subject }));
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}
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}
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self.add(subject.subscribe(subscriber));
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}
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function dispatchNext(arg) {
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const { value, subject } = arg;
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subject.next(value);
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subject.complete();
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}
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function dispatchError(arg) {
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const { err, subject } = arg;
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subject.error(err);
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}
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//# sourceMappingURL=BoundNodeCallbackObservable.js.map
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