查阅lib.es5.d.ts，被标记为@deprecated的接口一共有23处，包括：

• 全局接口2处
• String接口1处
• RegExp接口20处

废弃 escape / unescape

/**
 * Computes a new string in which certain characters have been replaced by a hexadecimal escape sequence.
 * @deprecated A legacy feature for browser compatibility
 * @param string A string value
 */
declare function escape(string: string): string;

/**
 * Computes a new string in which hexadecimal escape sequences are replaced with the character that it represents.
 * @deprecated A legacy feature for browser compatibility
 * @param string A string value
 */
declare function unescape(string: string): string;

这两个接口的功能，可以参考MDN的资料escape()和unescape()。

escape/unescape对宽字符进行重新编码，并做了特殊的标记。例如：

escape('中文')
// %u4E2D%u6587

粗略还原一下这个过程

'中文'.split('').map(s => '%u' + s.charCodeAt(0).toString(16)).join('')
// %u4e2d%u6587

当然，和encodeURIComponent一样，对于ASCII的字符集，并不会做重新编码。

废弃RegExp状态和compile方法

interface RegExp {
    // Non-standard extensions
    /** @deprecated A legacy feature for browser compatibility */
    compile(pattern: string, flags?: string): this;
}

interface RegExpConstructor {
    new(pattern: RegExp | string): RegExp;
    new(pattern: string, flags?: string): RegExp;
    (pattern: RegExp | string): RegExp;
    (pattern: string, flags?: string): RegExp;
    readonly prototype: RegExp;

    // Non-standard extensions
    /** @deprecated A legacy feature for browser compatibility */
    $1: string;
    /** @deprecated A legacy feature for browser compatibility */
    $2: string;
    /** @deprecated A legacy feature for browser compatibility */
    $3: string;
    /** @deprecated A legacy feature for browser compatibility */
    $4: string;
    /** @deprecated A legacy feature for browser compatibility */
    $5: string;
    /** @deprecated A legacy feature for browser compatibility */
    $6: string;
    /** @deprecated A legacy feature for browser compatibility */
    $7: string;
    /** @deprecated A legacy feature for browser compatibility */
    $8: string;
    /** @deprecated A legacy feature for browser compatibility */
    $9: string;
    /** @deprecated A legacy feature for browser compatibility */
    input: string;
    /** @deprecated A legacy feature for browser compatibility */
    $_: string;
    /** @deprecated A legacy feature for browser compatibility */
    lastMatch: string;
    /** @deprecated A legacy feature for browser compatibility */
    "$&": string;
    /** @deprecated A legacy feature for browser compatibility */
    lastParen: string;
    /** @deprecated A legacy feature for browser compatibility */
    "$+": string;
    /** @deprecated A legacy feature for browser compatibility */
    leftContext: string;
    /** @deprecated A legacy feature for browser compatibility */
    "$`": string;
    /** @deprecated A legacy feature for browser compatibility */
    rightContext: string;
    /** @deprecated A legacy feature for browser compatibility */
    "$'": string;
}

在RegExpConstructor中被废弃的各种属性中，最常用的是分组编组属性。例如：

if(/<(\w+)/.test('<div>')) {
    console.log(RegExp.$1)
}
// div

这种更关注规则是否匹配，对匹配结果不敏感的场景，用分组属性来获得匹配结果，使用上还是有一定便利的。

但这里有个特别容易踩到的坑，就是每次匹配执行后，分组属性都会有变化，必须非常小心地操作这个属性结果，尤其是有await/async的时候。

总的来说，这是一种stateness的情况，模式上不推荐，且容易进坑，虽然我个人觉得有点可惜，但通过废弃不好的模式，来避免程序员踩坑的做法，还是应当支持的。

另外的compile方法，原来的环境是编译正则后会有性能提升，但现在这个需求应该不多了。

废弃String的substr方法

    /**
     * Gets a substring beginning at the specified location and having the specified length.
     * @deprecated A legacy feature for browser compatibility
     * @param from The starting position of the desired substring. The index of the first character in the string is zero.
     * @param length The number of characters to include in the returned substring.
     */
    substr(from: number, length?: number): string;

很早之前就有推荐使用substring来替代substr，但我个人的思考习惯，更喜欢用substr。行吧。

以上。