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fix(throttle): now properly trailing throttles for individual values (#…
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…3505)

BREAKING CHANGES: This changes the behavior of throttle, in particular
throttling with both leading and trailing behaviors set to true, to more
closely match the throttling behavior of lodash and other libraries.
Throttling now starts immediately after any emission from the
observable, and values will not be double emitted for both leading and
trailing values

closes #2864
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@benlesh
benlesh committed Mar 30, 2018
1 parent 23566af commit 3db18d1
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Showing 2 changed files with 98 additions and 73 deletions.
94 changes: 61 additions & 33 deletions spec/operators/throttle-spec.ts
View file
Original file line number Diff line number Diff line change
Expand Up @@ -209,28 +209,24 @@ describe('Observable.prototype.throttle', () => {
});

it('should propagate error thrown from durationSelector function', () => {
const e1 = hot('abcdefabcdabcdefghabca| ');
const e1subs = '^ ! ';
const e2 = [cold('-----| '),
cold( '---| '),
cold( '-------| ')];
const e2subs = ['^ ! ',
' ^ ! '];
const expected = 'a-----a---# ';
const s1 = hot('--^--x--x--x--x--x--x--e--x--x--x--|');
const s1Subs = '^ !';
const n1 = cold( '----|');
const n1Subs = [' ^ ! ',
' ^ ! ',
' ^ ! '];
const exp = '---x-----x-----x-----(e#)';

let i = 0;
const result = e1.throttle(() => {
if (i === 2) {
throw 'error';
const result = s1.throttle(() => {
if (i++ === 3) {
throw new Error('lol');
}
return e2[i++];
return n1;
});

expectObservable(result).toBe(expected);
expectSubscriptions(e1.subscriptions).toBe(e1subs);
for (let j = 0; j < e2subs.length; j++) {
expectSubscriptions(e2[j].subscriptions).toBe(e2subs[j]);
}
expectObservable(result).toBe(exp, undefined, new Error('lol'));
expectSubscriptions(s1.subscriptions).toBe(s1Subs);
expectSubscriptions(n1.subscriptions).toBe(n1Subs);
});

it('should complete when source does not emit', () => {
Expand Down Expand Up @@ -353,37 +349,69 @@ describe('Observable.prototype.throttle', () => {

describe('throttle(fn, { leading: true, trailing: true })', () => {
asDiagram('throttle(fn, { leading: true, trailing: true })')('should immediately emit the first value in each time window', () => {
const e1 = hot('-a-xy-----b--x--cxxx--|');
const e1subs = '^ !';
const e2 = cold( '----| ');
const e2subs = [' ^ ! ',
' ^ ! ',
' ^ ! '];
const expected = '-a---y----b---x-c---x-|';
const e1 = hot('-a-xy-----b--x--cxxx------|');
const e1subs = '^ !';
const e2 = cold( '----| ');
const e2subs = [' ^ ! ',
' ^ ! ',
' ^ ! ',
' ^ ! ',
' ^ ! ',
' ^ !'];
const expected = '-a---y----b---x---x---x---|';

const result = e1.throttle(() => e2, { leading: true, trailing: true });

expectObservable(result).toBe(expected);
expectSubscriptions(e1.subscriptions).toBe(e1subs);
expectSubscriptions(e2.subscriptions).toBe(e2subs);
});

it('should work for individual values', () => {
const s1 = hot('-^-x------------------|');
const s1Subs = '^ !';
const n1 = cold( '------------------------|');
const n1Subs = [' ^ !'];
const exp = '--x------------------|';

const result = s1.throttle(() => n1, { leading: true, trailing: true });
expectObservable(result).toBe(exp);
expectSubscriptions(s1.subscriptions).toBe(s1Subs);
expectSubscriptions(n1.subscriptions).toBe(n1Subs);
});
});

describe('throttle(fn, { leading: false, trailing: true })', () => {
asDiagram('throttle(fn, { leading: false, trailing: true })')('should immediately emit the first value in each time window', () => {
const e1 = hot('-a-xy-----b--x--cxxx--|');
const e1subs = '^ !';
const e2 = cold( '----| ');
const e2subs = [' ^ ! ',
' ^ ! ',
' ^ ! '];
const expected = '-----y--------x-----x-|';
const e1 = hot('-a-xy-----b--x--cxxx------|');
const e1subs = '^ !';
const e2 = cold( '----| ');
const e2subs = [' ^ ! ',
' ^ ! ',
' ^ ! ',
' ^ ! ',
' ^ ! ',
' ^ !'];
const expected = '-a---y----b---x---x---x---|';

const result = e1.throttle(() => e2, { leading: false, trailing: true });
const result = e1.throttle(() => e2, { leading: true, trailing: true });

expectObservable(result).toBe(expected);
expectSubscriptions(e1.subscriptions).toBe(e1subs);
expectSubscriptions(e2.subscriptions).toBe(e2subs);
});

it('should work for individual values', () => {
const s1 = hot('-^-x------------------|');
const s1Subs = '^ !';
const n1 = cold( '------------------------|');
const n1Subs = [' ^ !'];
const exp = '--x------------------|';

const result = s1.throttle(() => n1, { leading: true, trailing: true });
expectObservable(result).toBe(exp);
expectSubscriptions(s1.subscriptions).toBe(s1Subs);
expectSubscriptions(n1.subscriptions).toBe(n1Subs);
});
});
});
77 changes: 37 additions & 40 deletions src/internal/operators/throttle.ts
View file
Original file line number Diff line number Diff line change
Expand Up @@ -83,38 +83,47 @@ class ThrottleOperator<T> implements Operator<T, T> {
* @extends {Ignored}
*/
class ThrottleSubscriber<T, R> extends OuterSubscriber<T, R> {
private throttled: Subscription;
private _trailingValue: T;
private _hasTrailingValue = false;
private _throttled: Subscription;
private _sendValue: T;
private _hasValue = false;

constructor(protected destination: Subscriber<T>,
private durationSelector: (value: T) => SubscribableOrPromise<any>,
private durationSelector: (value: T) => SubscribableOrPromise<number>,
private _leading: boolean,
private _trailing: boolean) {
super(destination);
}

protected _next(value: T): void {
if (this.throttled) {
if (this._trailing) {
this._hasTrailingValue = true;
this._trailingValue = value;
}
} else {
const duration = this.tryDurationSelector(value);
if (duration) {
this.add(this.throttled = subscribeToResult(this, duration));
}
this._hasValue = true;
this._sendValue = value;

if (!this._throttled) {
if (this._leading) {
this.destination.next(value);
if (this._trailing) {
this._hasTrailingValue = true;
this._trailingValue = value;
}
this.send();
} else {
this.throttle(value);
}
}
}

private send() {
const { _hasValue, _sendValue } = this;
if (_hasValue) {
this.destination.next(_sendValue);
this.throttle(_sendValue);
}
this._hasValue = false;
this._sendValue = null;
}

private throttle(value: T): void {
const duration = this.tryDurationSelector(value);
if (duration) {
this.add(this._throttled = subscribeToResult(this, duration));
}
}

private tryDurationSelector(value: T): SubscribableOrPromise<any> {
try {
return this.durationSelector(value);
Expand All @@ -124,37 +133,25 @@ class ThrottleSubscriber<T, R> extends OuterSubscriber<T, R> {
}
}

protected _unsubscribe() {
const { throttled, _trailingValue, _hasTrailingValue, _trailing } = this;

this._trailingValue = null;
this._hasTrailingValue = false;

if (throttled) {
this.remove(throttled);
this.throttled = null;
throttled.unsubscribe();
private throttlingDone() {
const { _throttled, _trailing } = this;
if (_throttled) {
_throttled.unsubscribe();
}
}
this._throttled = null;

private _sendTrailing() {
const { destination, throttled, _trailing, _trailingValue, _hasTrailingValue } = this;
if (throttled && _trailing && _hasTrailingValue) {
destination.next(_trailingValue);
this._trailingValue = null;
this._hasTrailingValue = false;
if (_trailing) {
this.send();
}
}

notifyNext(outerValue: T, innerValue: R,
outerIndex: number, innerIndex: number,
innerSub: InnerSubscriber<T, R>): void {
this._sendTrailing();
this._unsubscribe();
this.throttlingDone();
}

notifyComplete(): void {
this._sendTrailing();
this._unsubscribe();
this.throttlingDone();
}
}

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