javascript - Typescript 通用方法装饰器返回 Promise 作为值

Question

我正在尝试实现一个通用方法装饰器，它可以与原型(prototype)方法和实例方法一起使用。

基于:Typescript decorators not working with arrow functions

从下面的代码中可以看到，instanceMethod() 返回了一个 Promise。

有什么方法可以返回正确的值吗？

装饰器代码:

export function trace(verbose: boolean = false) {

    return (target: any, prop: string, descriptor?: TypedPropertyDescriptor<any>): any => {
        let fn
        let patchedFn

        if (descriptor) {
            fn = descriptor.value
        }

        return {
            configurable: true,
            enumerable: false,
            get() {
                if (!patchedFn) {
                    patchedFn = async (...args) => {
                        const ret = fn.call(this, ...args)
                        console.log(`typeof ret: ${typeof ret}`)
                        console.log(`return value: ${ret}`)
                        return ret
                    }
                }
                console.log(`get() patchedFn: ${patchedFn}`)
                return patchedFn
            },
            set(newFn) {
                console.log(`set() newFn: ${newFn}`)
                patchedFn = undefined
                fn = newFn
            },
        }

    }
}

测试类和测试代码:

class Greeter {

    @trace()
    public instanceMethod(s: string): string {
        return s
    }

    @trace()
    public async instanceAsyncMethod(s: string): Promise<string> {
        return s
    }

    @trace()
    public instanceArrowMethod = (s: string): string => {
        return s
    }

}

async function test() {
    const greeter = new Greeter()
    const result1 = greeter.instanceMethod('1')
    console.log(`* instanceMethod: ${result1}`) // should return '1', instead returns a Promise
    const result2 = await greeter.instanceAsyncMethod('2')
    console.log(`* instanceAsyncMethod: ${result2}`)
    const result3 = await greeter.instanceArrowMethod('3')
    console.log(`* instanceArrowMethod: ${result3}`)

}

test()

输出:

set() newFn: (s) => {
            return s;
        }
get() patchedFn: (...args) => __awaiter(this, void 0, void 0, function* () {
                        console.log(`typeof fn: ${typeof fn}`);
                        const ret = fn.call(this, ...args);
                        console.log(`typeof ret: ${typeof ret}`);
                        console.log(`return value: ${ret}`);
                        return ret;
                    })
typeof ret: string
return value: 1
* instanceMethod: [object Promise] <<<<<<<<<< The instance method is returning a Promise
get() patchedFn: (...args) => __awaiter(this, void 0, void 0, function* () {
                        console.log(`typeof fn: ${typeof fn}`);
                        const ret = fn.call(this, ...args);
                        console.log(`typeof ret: ${typeof ret}`);
                        console.log(`return value: ${ret}`);
                        return ret;
                    })
typeof ret: object
return value: [object Promise]
* instanceAsyncMethod: 2
get() patchedFn: (...args) => __awaiter(this, void 0, void 0, function* () {
                        console.log(`typeof fn: ${typeof fn}`);
                        const ret = fn.call(this, ...args);
                        console.log(`typeof ret: ${typeof ret}`);
                        console.log(`return value: ${ret}`);
                        return ret;
                    })
typeof ret: string
return value: 3
* instanceArrowMethod: 3

Answer 1

async 函数将始终返回一个 Promise。

您已将 patchedFn 定义为 async 函数，您必须进行修改以将其声明为普通函数，或者在调用方处 await(如果需要)。