@reactivex/rxjs
Version:
Reactive Extensions for modern JavaScript
221 lines • 9.41 kB
JavaScript
;
Object.defineProperty(exports, "__esModule", { value: true });
var Observable_1 = require("../Observable");
var AsyncSubject_1 = require("../AsyncSubject");
var map_1 = require("../operators/map");
var canReportError_1 = require("../util/canReportError");
var isScheduler_1 = require("../util/isScheduler");
var isArray_1 = require("../util/isArray");
/**
* Converts a Node.js-style callback API to a function that returns an
* Observable.
*
* <span class="informal">It's just like {@link bindCallback}, but the
* callback is expected to be of type `callback(error, result)`.</span>
*
* `bindNodeCallback` is not an operator because its input and output are not
* Observables. The input is a function `func` with some parameters, but the
* last parameter must be a callback function that `func` calls when it is
* done. The callback function is expected to follow Node.js conventions,
* where the first argument to the callback is an error object, signaling
* whether call was successful. If that object is passed to callback, it means
* something went wrong.
*
* The output of `bindNodeCallback` is a function that takes the same
* parameters as `func`, except the last one (the callback). When the output
* function is called with arguments, it will return an Observable.
* If `func` calls its callback with error parameter present, Observable will
* error with that value as well. If error parameter is not passed, Observable will emit
* second parameter. If there are more parameters (third and so on),
* Observable will emit an array with all arguments, except first error argument.
*
* Note that `func` will not be called at the same time output function is,
* but rather whenever resulting Observable is subscribed. By default call to
* `func` will happen synchronously after subscription, but that can be changed
* with proper `scheduler` provided as optional third parameter. {@link SchedulerLike}
* can also control when values from callback will be emitted by Observable.
* To find out more, check out documentation for {@link bindCallback}, where
* {@link SchedulerLike} works exactly the same.
*
* As in {@link bindCallback}, context (`this` property) of input function will be set to context
* of returned function, when it is called.
*
* After Observable emits value, it will complete immediately. This means
* even if `func` calls callback again, values from second and consecutive
* calls will never appear on the stream. If you need to handle functions
* that call callbacks multiple times, check out {@link fromEvent} or
* {@link fromEventPattern} instead.
*
* Note that `bindNodeCallback` can be used in non-Node.js environments as well.
* "Node.js-style" callbacks are just a convention, so if you write for
* browsers or any other environment and API you use implements that callback style,
* `bindNodeCallback` can be safely used on that API functions as well.
*
* Remember that Error object passed to callback does not have to be an instance
* of JavaScript built-in `Error` object. In fact, it does not even have to an object.
* Error parameter of callback function is interpreted as "present", when value
* of that parameter is truthy. It could be, for example, non-zero number, non-empty
* string or boolean `true`. In all of these cases resulting Observable would error
* with that value. This means usually regular style callbacks will fail very often when
* `bindNodeCallback` is used. If your Observable errors much more often then you
* would expect, check if callback really is called in Node.js-style and, if not,
* switch to {@link bindCallback} instead.
*
* Note that even if error parameter is technically present in callback, but its value
* is falsy, it still won't appear in array emitted by Observable.
*
* ## Examples
* ### Read a file from the filesystem and get the data as an Observable
* ```ts
* import * as fs from 'fs';
* const readFileAsObservable = bindNodeCallback(fs.readFile);
* const result = readFileAsObservable('./roadNames.txt', 'utf8');
* result.subscribe(x => console.log(x), e => console.error(e));
* ```
*
* ### Use on function calling callback with multiple arguments
* ```ts
* someFunction((err, a, b) => {
* console.log(err); // null
* console.log(a); // 5
* console.log(b); // "some string"
* });
* const boundSomeFunction = bindNodeCallback(someFunction);
* boundSomeFunction()
* .subscribe(value => {
* console.log(value); // [5, "some string"]
* });
* ```
*
* ### Use on function calling callback in regular style
* ```ts
* someFunction(a => {
* console.log(a); // 5
* });
* const boundSomeFunction = bindNodeCallback(someFunction);
* boundSomeFunction()
* .subscribe(
* value => {} // never gets called
* err => console.log(err) // 5
* );
* ```
*
* @see {@link bindCallback}
* @see {@link from}
*
* @param {function} func Function with a Node.js-style callback as the last parameter.
* @param {SchedulerLike} [scheduler] The scheduler on which to schedule the
* callbacks.
* @return {function(...params: *): Observable} A function which returns the
* Observable that delivers the same values the Node.js callback would
* deliver.
* @name bindNodeCallback
*/
function bindNodeCallback(callbackFunc, resultSelector, scheduler) {
if (resultSelector) {
if (isScheduler_1.isScheduler(resultSelector)) {
scheduler = resultSelector;
}
else {
// DEPRECATED PATH
return function () {
var args = [];
for (var _i = 0; _i < arguments.length; _i++) {
args[_i] = arguments[_i];
}
return bindNodeCallback(callbackFunc, scheduler).apply(void 0, args).pipe(map_1.map(function (args) { return isArray_1.isArray(args) ? resultSelector.apply(void 0, args) : resultSelector(args); }));
};
}
}
return function () {
var args = [];
for (var _i = 0; _i < arguments.length; _i++) {
args[_i] = arguments[_i];
}
var params = {
subject: undefined,
args: args,
callbackFunc: callbackFunc,
scheduler: scheduler,
context: this,
};
return new Observable_1.Observable(function (subscriber) {
var context = params.context;
var subject = params.subject;
if (!scheduler) {
if (!subject) {
subject = params.subject = new AsyncSubject_1.AsyncSubject();
var handler = function () {
var innerArgs = [];
for (var _i = 0; _i < arguments.length; _i++) {
innerArgs[_i] = arguments[_i];
}
var err = innerArgs.shift();
if (err) {
subject.error(err);
return;
}
subject.next(innerArgs.length <= 1 ? innerArgs[0] : innerArgs);
subject.complete();
};
try {
callbackFunc.apply(context, args.concat([handler]));
}
catch (err) {
if (canReportError_1.canReportError(subject)) {
subject.error(err);
}
else {
console.warn(err);
}
}
}
return subject.subscribe(subscriber);
}
else {
return scheduler.schedule(dispatch, 0, { params: params, subscriber: subscriber, context: context });
}
});
};
}
exports.bindNodeCallback = bindNodeCallback;
function dispatch(state) {
var _this = this;
var params = state.params, subscriber = state.subscriber, context = state.context;
var callbackFunc = params.callbackFunc, args = params.args, scheduler = params.scheduler;
var subject = params.subject;
if (!subject) {
subject = params.subject = new AsyncSubject_1.AsyncSubject();
var handler = function () {
var innerArgs = [];
for (var _i = 0; _i < arguments.length; _i++) {
innerArgs[_i] = arguments[_i];
}
var err = innerArgs.shift();
if (err) {
_this.add(scheduler.schedule(dispatchError, 0, { err: err, subject: subject }));
}
else {
var value = innerArgs.length <= 1 ? innerArgs[0] : innerArgs;
_this.add(scheduler.schedule(dispatchNext, 0, { value: value, subject: subject }));
}
};
try {
callbackFunc.apply(context, args.concat([handler]));
}
catch (err) {
this.add(scheduler.schedule(dispatchError, 0, { err: err, subject: subject }));
}
}
this.add(subject.subscribe(subscriber));
}
function dispatchNext(arg) {
var value = arg.value, subject = arg.subject;
subject.next(value);
subject.complete();
}
function dispatchError(arg) {
var err = arg.err, subject = arg.subject;
subject.error(err);
}
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