es6/operator/distinctUntilChanged.js

import { Subscriber } from '../Subscriber';
import { tryCatch } from '../util/tryCatch';
import { errorObject } from '../util/errorObject';
/* tslint:enable:max-line-length */
/**
 * 返回 Observable，它发出源 Observable 发出的所有与前一项不相同的项。
 *
 * 如果提供了 compare 函数，那么每一项都会调用它来检验是否应该发出这个值。
 *
 * 如果没有提供 compare 函数，默认使用相等检查。
 *
 * @example <caption>使用数字的简单示例</caption>
 * Observable.of(1, 1, 2, 2, 2, 1, 1, 2, 3, 3, 4)
 *   .distinctUntilChanged()
 *   .subscribe(x => console.log(x)); // 1, 2, 1, 2, 3, 4
 *
 * @example <caption>使用 compare 函数的示例</caption>
 * interface Person {
 *    age: number,
 *    name: string
 * }
 *
 * Observable.of<Person>(
 *     { age: 4, name: 'Foo'},
 *     { age: 7, name: 'Bar'},
 *     { age: 5, name: 'Foo'})
 *     { age: 6, name: 'Foo'})
 *     .distinctUntilChanged((p: Person, q: Person) => p.name === q.name)
 *     .subscribe(x => console.log(x));
 *
 * // 显示：
 * // { age: 4, name: 'Foo' }
 * // { age: 7, name: 'Bar' }
 * // { age: 5, name: 'Foo' }
 *
 * @see {@link distinct}
 * @see {@link distinctUntilKeyChanged}
 *
 * @param {function} [compare] 可选比较函数，用来检验当前项与源中的前一项是否相同。
 * @return {Observable} 该 Observable 发出从源 Observable 中得到的与前一项不同的值。
 * @method distinctUntilChanged
 * @owner Observable
 */
export function distinctUntilChanged(compare, keySelector) {
    return this.lift(new DistinctUntilChangedOperator(compare, keySelector));
}
class DistinctUntilChangedOperator {
    constructor(compare, keySelector) {
        this.compare = compare;
        this.keySelector = keySelector;
    }
    call(subscriber, source) {
        return source.subscribe(new DistinctUntilChangedSubscriber(subscriber, this.compare, this.keySelector));
    }
}
/**
 * We need this JSDoc comment for affecting ESDoc.
 * @ignore
 * @extends {Ignored}
 */
class DistinctUntilChangedSubscriber extends Subscriber {
    constructor(destination, compare, keySelector) {
        super(destination);
        this.keySelector = keySelector;
        this.hasKey = false;
        if (typeof compare === 'function') {
            this.compare = compare;
        }
    }
    compare(x, y) {
        return x === y;
    }
    _next(value) {
        const keySelector = this.keySelector;
        let key = value;
        if (keySelector) {
            key = tryCatch(this.keySelector)(value);
            if (key === errorObject) {
                return this.destination.error(errorObject.e);
            }
        }
        let result = 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);
        }
    }
}
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