import { isScheduler } from '../util/isScheduler'; import { isArray } from '../util/isArray'; import { ArrayObservable } from './ArrayObservable'; import { CombineLatestOperator } from '../operators/combineLatest'; /* tslint:enable:max-line-length */ /** * Combines multiple Observables to create an Observable whose values are * calculated from the latest values of each of its input Observables. * * Whenever any input Observable emits a value, it * computes a formula using the latest values from all the inputs, then emits * the output of that formula. * * * * `combineLatest` combines the values from all the Observables passed as * arguments. This is done by subscribing to each Observable in order and, * whenever any Observable emits, collecting an array of the most recent * values from each Observable. So if you pass `n` Observables to operator, * returned Observable will always emit an array of `n` values, in order * corresponding to order of passed Observables (value from the first Observable * on the first place and so on). * * Static version of `combineLatest` accepts either an array of Observables * or each Observable can be put directly as an argument. Note that array of * Observables is good choice, if you don't know beforehand how many Observables * you will combine. Passing empty array will result in Observable that * completes immediately. * * To ensure output array has always the same length, `combineLatest` will * actually wait for all input Observables to emit at least once, * before it starts emitting results. This means if some Observable emits * values before other Observables started emitting, all that values but last * will be lost. On the other hand, is some Observable does not emit value but * completes, resulting Observable will complete at the same moment without * emitting anything, since it will be now impossible to include value from * completed Observable in resulting array. Also, if some input Observable does * not emit any value and never completes, `combineLatest` will also never emit * and never complete, since, again, it will wait for all streams to emit some * value. * * If at least one Observable was passed to `combineLatest` and all passed Observables * emitted something, resulting Observable will complete when all combined * streams complete. So even if some Observable completes, result of * `combineLatest` will still emit values when other Observables do. In case * of completed Observable, its value from now on will always be the last * emitted value. On the other hand, if any Observable errors, `combineLatest` * will error immediately as well, and all other Observables will be unsubscribed. * * `combineLatest` accepts as optional parameter `project` function, which takes * as arguments all values that would normally be emitted by resulting Observable. * `project` can return any kind of value, which will be then emitted by Observable * instead of default array. Note that `project` does not take as argument that array * of values, but values themselves. That means default `project` can be imagined * as function that takes all its arguments and puts them into an array. * * * @example Combine two timer Observables * const firstTimer = Rx.Observable.timer(0, 1000); // emit 0, 1, 2... after every second, starting from now * const secondTimer = Rx.Observable.timer(500, 1000); // emit 0, 1, 2... after every second, starting 0,5s from now * const combinedTimers = Rx.Observable.combineLatest(firstTimer, secondTimer); * combinedTimers.subscribe(value => console.log(value)); * // Logs * // [0, 0] after 0.5s * // [1, 0] after 1s * // [1, 1] after 1.5s * // [2, 1] after 2s * * * @example Combine an array of Observables * const observables = [1, 5, 10].map( * n => Rx.Observable.of(n).delay(n * 1000).startWith(0) // emit 0 and then emit n after n seconds * ); * const combined = Rx.Observable.combineLatest(observables); * combined.subscribe(value => console.log(value)); * // Logs * // [0, 0, 0] immediately * // [1, 0, 0] after 1s * // [1, 5, 0] after 5s * // [1, 5, 10] after 10s * * * @example Use project function to dynamically calculate the Body-Mass Index * var weight = Rx.Observable.of(70, 72, 76, 79, 75); * var height = Rx.Observable.of(1.76, 1.77, 1.78); * var bmi = Rx.Observable.combineLatest(weight, height, (w, h) => w / (h * h)); * bmi.subscribe(x => console.log('BMI is ' + x)); * * // With output to console: * // BMI is 24.212293388429753 * // BMI is 23.93948099205209 * // BMI is 23.671253629592222 * * * @see {@link combineAll} * @see {@link merge} * @see {@link withLatestFrom} * * @param {ObservableInput} observable1 An input Observable to combine with other Observables. * @param {ObservableInput} observable2 An input Observable to combine with other Observables. * More than one input Observables may be given as arguments * or an array of Observables may be given as the first argument. * @param {function} [project] An optional function to project the values from * the combined latest values into a new value on the output Observable. * @param {Scheduler} [scheduler=null] The IScheduler to use for subscribing to * each input Observable. * @return {Observable} An Observable of projected values from the most recent * values from each input Observable, or an array of the most recent values from * each input Observable. * @static true * @name combineLatest * @owner Observable */ export function combineLatest(...observables) { let project = null; let scheduler = null; if (isScheduler(observables[observables.length - 1])) { scheduler = observables.pop(); } if (typeof observables[observables.length - 1] === 'function') { project = observables.pop(); } // if the first and only other argument besides the resultSelector is an array // assume it's been called with `combineLatest([obs1, obs2, obs3], project)` if (observables.length === 1 && isArray(observables[0])) { observables = observables[0]; } return new ArrayObservable(observables, scheduler).lift(new CombineLatestOperator(project)); } //# sourceMappingURL=combineLatest.js.map