TypeScript 学习笔记：属性索引器

export interface StringValidator {    isAcceptable(s: string): boolean;}const lettersRegexp = /^[A-Za-z]+$/;export class LettersOnlyValidator implements StringValidator {    isAcceptable(s: string) {        return lettersRegexp.test(s);    }}const numberRegexp = /^[0-9]+$/;export class ZipCodeValidator implements StringValidator {    isAcceptable(s: string) {        return s.length === 5 && numberRegexp.test(s);    }}// 开始测试let strings = ["Hello", "98052", "101"];// Validators to uselet validators: { [key: string]: StringValidator; } = {};validators["邮政编码"] = new ZipCodeValidator();validators["纯字符"] = new LettersOnlyValidator();// Show whether each string passed each validatorstrings.forEach(stringItem => {    for (let valName in validators) {         console.log(`"${stringItem}" - ${validators[valName].isAcceptable(stringItem) ? "匹配" : "不匹配"} ${valName}`);    }});

运行结果如下：

"Hello" - 不匹配 邮政编码"Hello" - 匹配 纯字符"98052" - 匹配 邮政编码"98052" - 不匹配 纯字符"101" - 不匹配 邮政编码"101" - 不匹配 纯字符

我是真搞不懂这一句，太奇妙.... 

1. let validators: { [key: string]: StringValidator; } = {};