最初，我对DatePipe进行了简单扩展，以转换标准（YYYYMMDD格式）中的日期值，以便Angular中的DatePipe可以使用它。

export class SlsDatePipe extends DatePipe implements PipeTransform {
    constructor(Locale:string) {
        super(Locale);
    }

    /**
     * Convert the data from the numeric YYYYMMDD to the Javascript date format
     * @param DateValue SLS Formatted number in the YYYYMMDD style
     * @param args Angular Date Pipe args to control the output format
     * @returns Text output following the Javascript date() formats
     */
    public transform(DateValue:number, args:string):string | null {
    
        const DateString:string = DateValue.toString();
        const Year:number  = parseInt(DateString.substr(0, 4), 10);
        const Month:number = parseInt(DateString.substr(4, 2), 10) - 1;
        const Day:number   = parseInt(DateString.substr(6, 2), 10);
        const DateObject:Date = new Date(Year, Month, Day);

        return super.transform(DateObject, args);
}

该类中还进行了其他检查以确保格式正确，等等，但是问题的基本知识在那里。这在Angular 10中有效。我刚刚更新到Angular 11，现在代码在转换中产生错误：

error TS2416: Property 'transform' in type 'SlsTimePipe' is not assignable to the same property in base type 'DatePipe'.
    Type '(TimeValue: number, args: string) => string' is not assignable to type '{ (value: string | number | Date, format?: string, timezone?: string, locale?: string): string; (value: null,
    format?: string, timezone?: string, locale?: string): null; (value: string | number | Date, for mat?: string, timezone?: string, locale?: string): string; }'.
    Type 'string' is not assignable to type 'null'.