operator習作

filter-map.ts

import { strict as assert } from 'assert';
import { Operator, OperatorFunction, Subscriber } from "rxjs";

export type FilterMap<T, U> = (e: T, index: number) => U | null;

class FilterMapSubscriber<T, U> extends Subscriber<T> {
    private count = 0;
    private readonly thisArg: any;
    constructor(
        destination: Subscriber<U>,
        private project: FilterMap<T, U>,
        thisArg: any,
    ) {
        super(destination);
        this.thisArg = thisArg ?? this;
    }
    protected _next(value: T) {
        let result: U | null;
        try {
            result = this.project.call(this.thisArg, value, this.count++);
        } catch (err) {
            assert(this.destination.error);
            this.destination.error(err);
            return;
        }
        if (result !== null) {
            assert(this.destination.next);
            this.destination.next(result);
        }
    }
}

class FilterMapOperator<T, U> implements Operator<T, U> {
    constructor(private project: FilterMap<T, U>, private thisArg: any) {
    }
    call(subscriber: Subscriber<U>, source: any): any {
        return source.subscribe(new FilterMapSubscriber(subscriber, this.project, this.thisArg));
    }
}

export const filterMap = <T, U>(project: FilterMap<T, U>, thisArg?: any): OperatorFunction<T, U> => {
    return (source) => {
        return source.lift(new FilterMapOperator(project, thisArg));
    };
};