ValidationRule.ts

export class ValidationRule {
    private static _validationRulesMap: Map < string, ValidationRule > ;
    public static get validationRulesMap() {
        if (!ValidationRule._validationRulesMap) {
            ValidationRule._validationRulesMap = new Map < string, ValidationRule > ();
        }
        return ValidationRule._validationRulesMap;
    }
    public static required = new ValidationRule('REQUIRED', Validators.required);
    private constructor(private name: string, public validationFn: (control: AbstractControl) => ValidationErrors | null) {
        ValidationRule.validationRulesMap.set(name, this);
    }
    toString() {
        return this.name;
    }
}