能否为TypeScript 3.9.6兼容抽象构造函数类型定义？

问题描述 #

需要在TypeScript 3.9.6环境中使用以下类型定义：

export type Class<
    _CtorArgs extends any[] = any[],
    InstanceType = {},
    StaticType = {},
    _IsAbstract = false
> = (abstract new (...args: any[]) => InstanceType) & StaticType;

但编译时出现一系列语法错误：

dir/polyfills/mixin-polyfill/types.d.ts:40:15 - error TS1005: ')' expected.

40 > = (abstract new (...args: any[]) => InstanceType) & StaticType;
                 ~~~

dir/polyfills/mixin-polyfill/types.d.ts:40:20 - error TS1109: Expression expected.

40 > = (abstract new (...args: any[]) => InstanceType) & StaticType;
                      ~~~

dir/polyfills/mixin-polyfill/types.d.ts:40:33 - error TS1011: An element access expression should take an argument.

40 > = (abstract new (...args: any[]) => InstanceType) & StaticType;


dir/polyfills/mixin-polyfill/types.d.ts:40:34 - error TS1005: ';' expected.

40 > = (abstract new (...args: any[]) => InstanceType) & StaticType;
                                    ~

dir/polyfills/mixin-polyfill/types.d.ts:40:36 - error TS1128: Declaration or statement expected.

40 > = (abstract new (...args: any[]) => InstanceType) & StaticType;
                                      ~~

dir/polyfills/mixin-polyfill/types.d.ts:40:51 - error TS1005: ';' expected.

40 > = (abstract new (...args: any[]) => InstanceType) & StaticType;
                                                     ~

dir/polyfills/mixin-polyfill/types.d.ts:40:53 - error TS1109: Expression expected.

40 > = (abstract new (...args: any[]) => InstanceType) & StaticType;

错误原因 #

这些错误的核心原因是：TypeScript 3.9.6不支持在构造签名中使用abstract关键字。这个语法特性是TypeScript 4.2版本才引入的，因此在3.9.6版本中会触发语法解析错误。

适配方案 #

我们可以通过条件类型区分普通类和抽象类的类型定义，绕过TS3.9.6的语法限制，同时保留原类型的核心功能：

export type Class<
    _CtorArgs extends any[] = any[],
    InstanceType = {},
    StaticType = {},
    _IsAbstract = false
> = _IsAbstract extends true
    ? // 抽象类类型：包含实例原型和静态成员，不能直接实例化
      ({ prototype: InstanceType } & StaticType)
    : // 普通类类型：保留可实例化的构造签名
      (new (...args: _CtorArgs) => InstanceType) & StaticType;

方案说明 #

• 当_IsAbstract为true时，用{ prototype: InstanceType }表示抽象类的核心特征（拥有实例原型但无法直接new），同时合并静态成员类型StaticType。
• 当_IsAbstract为false时，保留原有的可实例化构造签名，确保普通类可以被正确实例化并约束参数类型。
• 该定义完全兼容TS3.9.6的语法规则，同时保留了原类型对实例类型、静态类型、构造参数的约束能力。

内容的提问来源于stack exchange，提问作者Kris