distinctUntilChanged.ts
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import { Operator } from '../Operator';
import { Subscriber } from '../Subscriber';
import { tryCatch } from '../util/tryCatch';
import { errorObject } from '../util/errorObject';
import { Observable } from '../Observable';
import { TeardownLogic } from '../Subscription';
/* tslint:disable:max-line-length */
export function distinctUntilChanged<T>(this: Observable<T>, compare?: (x: T, y: T) => boolean): Observable<T>;
export function distinctUntilChanged<T, K>(this: Observable<T>, compare: (x: K, y: K) => boolean, keySelector: (x: T) => K): Observable<T>;
/* tslint:disable:max-line-length */
/**
* Returns an Observable that emits all items emitted by the source Observable that are distinct by comparison from the previous item.
* If a comparator function is provided, then it will be called for each item to test for whether or not that value should be emitted.
* If a comparator function is not provided, an equality check is used by default.
* @param {function} [compare] optional comparison function called to test if an item is distinct from the previous item in the source.
* @return {Observable} an Observable that emits items from the source Observable with distinct values.
* @method distinctUntilChanged
* @owner Observable
*/
export function distinctUntilChanged<T, K>(this: Observable<T>, compare?: (x: K, y: K) => boolean, keySelector?: (x: T) => K): Observable<T> {
return this.lift(new DistinctUntilChangedOperator<T, K>(compare, keySelector));
}
class DistinctUntilChangedOperator<T, K> implements Operator<T, T> {
constructor(private compare: (x: K, y: K) => boolean,
private keySelector: (x: T) => K) {
}
call(subscriber: Subscriber<T>, source: any): TeardownLogic {
return source.subscribe(new DistinctUntilChangedSubscriber(subscriber, this.compare, this.keySelector));
}
}
/**
* We need this JSDoc comment for affecting ESDoc.
* @ignore
* @extends {Ignored}
*/
class DistinctUntilChangedSubscriber<T, K> extends Subscriber<T> {
private key: K;
private hasKey: boolean = false;
constructor(destination: Subscriber<T>,
compare: (x: K, y: K) => boolean,
private keySelector: (x: T) => K) {
super(destination);
if (typeof compare === 'function') {
this.compare = compare;
}
}
private compare(x: any, y: any): boolean {
return x === y;
}
protected _next(value: T): void {
const keySelector = this.keySelector;
let key: any = value;
if (keySelector) {
key = tryCatch(this.keySelector)(value);
if (key === errorObject) {
return this.destination.error(errorObject.e);
}
}
let result: any = false;
if (this.hasKey) {
result = tryCatch(this.compare)(this.key, key);
if (result === errorObject) {
return this.destination.error(errorObject.e);
}
} else {
this.hasKey = true;
}
if (Boolean(result) === false) {
this.key = key;
this.destination.next(value);
}
}
}