Question

我正在尝试理解TypeScript装饰器（特别是属性），并根据我看到的一些示例提出了以下代码：

decorator.ts

export function logProperty(target: any, key: string) {

  let val = this[key];

  const getter = () => {
    console.log(`Get: ${key} => ${val}`);
    return val;
  };

  const setter = (newVal) => {
    console.log(`Set: ${key} => ${newVal}`);
    val = newVal;
  };

  if (delete this[key]) {
    Object.defineProperty(target, key, {
      get: getter,
      set: setter,
      enumerable: true,
      configurable: true
    });
  }
}

main.ts

import { logProperty } from './decorators';

class Person {
  @logProperty
  firstName: string;

  @logProperty
  lastName: string;

  constructor(firstName: string, lastName: string) {
    this.firstName = firstName;
    this.lastName = lastName;
  }
}

const foo = new Person('Foo', 'Bar');

我的问题是，当我尝试运行时，我得到：

TypeError：无法读取未定义的属性“firstName”

似乎this的值未定义。我错过了什么？

作为参考，我的tsconfig.json有：

"target": "es5"
"experimentalDecorators": true
"strict": false

更新8/27 似乎只有在装饰器位于不同的.ts文件中时才会出现此问题。如果将装饰器放在另一个文件中并从另一个文件导入，则会发生错误。但是，将它们全部放在同一个文件中不会导致问题。我只是误解了this如何被解释？

Answer 1

tl; dr：我不确定为什么OP的配置不起作用;它现在看起来很漂亮。请参阅下面的一些蛮力测试。

猜测

我想知道你是不是以某种方式选错了tsconfig。我看了your repo's tsconfig，看起来很正确。有没有机会另一个配置文件感染这些运行？我看到there were no automated tests there。

测试

我今天遇到了类似的问题，并以OP作为蓝图汇总a quick test。我提取了编译器选项from the official docs。

`decorators.ts`

export function logProperty(target: any, key: string) {

    let val = this[key];

    const getter = () => {
        console.log(`Get: ${key} => ${val}`);
        return val;
    };

    const setter = (newVal) => {
        console.log(`Set: ${key} => ${newVal}`);
        val = newVal;
    };

    if (delete this[key]) {
        Object.defineProperty(target, key, {
            get: getter,
            set: setter,
            enumerable: true,
            configurable: true
        });
    }
}

`main.ts`

import { logProperty } from './decorators';

class Person {
    @logProperty
    firstName: string;

    @logProperty
    lastName: string;

    constructor(firstName: string, lastName: string) {
        this.firstName = firstName;
        this.lastName = lastName;
    }
}

const foo = new Person('Foo', 'Bar');

function logProperty2(target: any, key: string) {

    let val = this[key];

    const getter = () => {
        console.log(`Get: ${key} => ${val}`);
        return val;
    };

    const setter = (newVal) => {
        console.log(`Set: ${key} => ${newVal}`);
        val = newVal;
    };

    if (delete this[key]) {
        Object.defineProperty(target, key, {
            get: getter,
            set: setter,
            enumerable: true,
            configurable: true
        });
    }
}

class Person2 {
    @logProperty2
    firstName: string;

    @logProperty2
    lastName: string;

    constructor(firstName: string, lastName: string) {
        this.firstName = firstName;
        this.lastName = lastName;
    }
}

const foo2 = new Person2('Foo', 'Bar');

`index.ts`

import * as assert from "assert";
import * as shelljs from "shelljs";

const MODULE_GENERATION = [
    "CommonJS",
    "AMD",
    "System",
    "UMD",
    "ES6",
    "ES2015",
    "ESNext",
];

const TARGETS = [
    "ES5",
    "ES2015",
    "ES2016",
    "ES2017"
]

shelljs.exec("tsc --target 'ES5' --module 'None' --strict main.ts", { silent: true });
assert.ok(shelljs.error());
shelljs.exec("tsc --target 'ES5' --module 'None' main.ts", { silent: true });
assert.ok(shelljs.error());

for (const moduleGeneration of MODULE_GENERATION) {
    console.log(`Testing module generation: ${moduleGeneration}`);
    for (const target of TARGETS) {
        console.log(`  Building for ${target}`);
        for (const strict of [true, false]) {
            console.log(`    Strict mode: ${strict ? 'en' : 'dis'}abled`)
            const command = (
                `tsc` +
                ` --module '${moduleGeneration}'` +
                ` --experimentalDecorators` +
                ` --target '${target}'` +
                ` ${strict ? "--strict" : ""}` +
                ` main.ts`
            );
            const output = shelljs.exec(
                command,
                { silent: true },
            );
            let symbol;
            if (strict) {
                assert.ok(shelljs.error());
                symbol = '✖'
            } else {
                assert.strictEqual(0, output.code);
                symbol = '✓'
            }
            console.log(`      ${symbol} ${command}`);
        }
    }
}

结果

您可以看到完整版on Travis。

Testing module generation: CommonJS
  Building for ES5
    Strict mode: enabled
      ✖ tsc --module 'CommonJS' --experimentalDecorators --target 'ES5' --strict main.ts
    Strict mode: disabled
      ✓ tsc --module 'CommonJS' --experimentalDecorators --target 'ES5'  main.ts
  Building for ES2015
    Strict mode: enabled
      ✖ tsc --module 'CommonJS' --experimentalDecorators --target 'ES2015' --strict main.ts
    Strict mode: disabled
      ✓ tsc --module 'CommonJS' --experimentalDecorators --target 'ES2015'  main.ts
  Building for ES2016
    Strict mode: enabled
      ✖ tsc --module 'CommonJS' --experimentalDecorators --target 'ES2016' --strict main.ts
    Strict mode: disabled
      ✓ tsc --module 'CommonJS' --experimentalDecorators --target 'ES2016'  main.ts
  Building for ES2017
    Strict mode: enabled
      ✖ tsc --module 'CommonJS' --experimentalDecorators --target 'ES2017' --strict main.ts
    Strict mode: disabled
      ✓ tsc --module 'CommonJS' --experimentalDecorators --target 'ES2017'  main.ts
Testing module generation: AMD
  Building for ES5
    Strict mode: enabled
      ✖ tsc --module 'AMD' --experimentalDecorators --target 'ES5' --strict main.ts
    Strict mode: disabled
      ✓ tsc --module 'AMD' --experimentalDecorators --target 'ES5'  main.ts
  Building for ES2015
    Strict mode: enabled
      ✖ tsc --module 'AMD' --experimentalDecorators --target 'ES2015' --strict main.ts
    Strict mode: disabled
      ✓ tsc --module 'AMD' --experimentalDecorators --target 'ES2015'  main.ts
  Building for ES2016
    Strict mode: enabled
      ✖ tsc --module 'AMD' --experimentalDecorators --target 'ES2016' --strict main.ts
    Strict mode: disabled
      ✓ tsc --module 'AMD' --experimentalDecorators --target 'ES2016'  main.ts
  Building for ES2017
    Strict mode: enabled
      ✖ tsc --module 'AMD' --experimentalDecorators --target 'ES2017' --strict main.ts
    Strict mode: disabled
      ✓ tsc --module 'AMD' --experimentalDecorators --target 'ES2017'  main.ts
Testing module generation: System
  Building for ES5
    Strict mode: enabled
      ✖ tsc --module 'System' --experimentalDecorators --target 'ES5' --strict main.ts
    Strict mode: disabled
      ✓ tsc --module 'System' --experimentalDecorators --target 'ES5'  main.ts
  Building for ES2015
    Strict mode: enabled
      ✖ tsc --module 'System' --experimentalDecorators --target 'ES2015' --strict main.ts
    Strict mode: disabled
      ✓ tsc --module 'System' --experimentalDecorators --target 'ES2015'  main.ts
  Building for ES2016
    Strict mode: enabled
      ✖ tsc --module 'System' --experimentalDecorators --target 'ES2016' --strict main.ts
    Strict mode: disabled
      ✓ tsc --module 'System' --experimentalDecorators --target 'ES2016'  main.ts
  Building for ES2017
    Strict mode: enabled
      ✖ tsc --module 'System' --experimentalDecorators --target 'ES2017' --strict main.ts
    Strict mode: disabled
      ✓ tsc --module 'System' --experimentalDecorators --target 'ES2017'  main.ts
Testing module generation: UMD
  Building for ES5
    Strict mode: enabled
      ✖ tsc --module 'UMD' --experimentalDecorators --target 'ES5' --strict main.ts
    Strict mode: disabled
      ✓ tsc --module 'UMD' --experimentalDecorators --target 'ES5'  main.ts
  Building for ES2015
    Strict mode: enabled
      ✖ tsc --module 'UMD' --experimentalDecorators --target 'ES2015' --strict main.ts
    Strict mode: disabled
      ✓ tsc --module 'UMD' --experimentalDecorators --target 'ES2015'  main.ts
  Building for ES2016
    Strict mode: enabled
      ✖ tsc --module 'UMD' --experimentalDecorators --target 'ES2016' --strict main.ts
    Strict mode: disabled
      ✓ tsc --module 'UMD' --experimentalDecorators --target 'ES2016'  main.ts
  Building for ES2017
    Strict mode: enabled
      ✖ tsc --module 'UMD' --experimentalDecorators --target 'ES2017' --strict main.ts
    Strict mode: disabled
      ✓ tsc --module 'UMD' --experimentalDecorators --target 'ES2017'  main.ts
Testing module generation: ES6
  Building for ES5
    Strict mode: enabled
      ✖ tsc --module 'ES6' --experimentalDecorators --target 'ES5' --strict main.ts
    Strict mode: disabled
      ✓ tsc --module 'ES6' --experimentalDecorators --target 'ES5'  main.ts
  Building for ES2015
    Strict mode: enabled
      ✖ tsc --module 'ES6' --experimentalDecorators --target 'ES2015' --strict main.ts
    Strict mode: disabled
      ✓ tsc --module 'ES6' --experimentalDecorators --target 'ES2015'  main.ts
  Building for ES2016
    Strict mode: enabled
      ✖ tsc --module 'ES6' --experimentalDecorators --target 'ES2016' --strict main.ts
    Strict mode: disabled
      ✓ tsc --module 'ES6' --experimentalDecorators --target 'ES2016'  main.ts
  Building for ES2017
    Strict mode: enabled
      ✖ tsc --module 'ES6' --experimentalDecorators --target 'ES2017' --strict main.ts
    Strict mode: disabled
      ✓ tsc --module 'ES6' --experimentalDecorators --target 'ES2017'  main.ts
Testing module generation: ES2015
  Building for ES5
    Strict mode: enabled
      ✖ tsc --module 'ES2015' --experimentalDecorators --target 'ES5' --strict main.ts
    Strict mode: disabled
      ✓ tsc --module 'ES2015' --experimentalDecorators --target 'ES5'  main.ts
  Building for ES2015
    Strict mode: enabled
      ✖ tsc --module 'ES2015' --experimentalDecorators --target 'ES2015' --strict main.ts
    Strict mode: disabled
      ✓ tsc --module 'ES2015' --experimentalDecorators --target 'ES2015'  main.ts
  Building for ES2016
    Strict mode: enabled
      ✖ tsc --module 'ES2015' --experimentalDecorators --target 'ES2016' --strict main.ts
    Strict mode: disabled
      ✓ tsc --module 'ES2015' --experimentalDecorators --target 'ES2016'  main.ts
  Building for ES2017
    Strict mode: enabled
      ✖ tsc --module 'ES2015' --experimentalDecorators --target 'ES2017' --strict main.ts
    Strict mode: disabled
      ✓ tsc --module 'ES2015' --experimentalDecorators --target 'ES2017'  main.ts
Testing module generation: ESNext
  Building for ES5
    Strict mode: enabled
      ✖ tsc --module 'ESNext' --experimentalDecorators --target 'ES5' --strict main.ts
    Strict mode: disabled
      ✓ tsc --module 'ESNext' --experimentalDecorators --target 'ES5'  main.ts
  Building for ES2015
    Strict mode: enabled
      ✖ tsc --module 'ESNext' --experimentalDecorators --target 'ES2015' --strict main.ts
    Strict mode: disabled
      ✓ tsc --module 'ESNext' --experimentalDecorators --target 'ES2015'  main.ts
  Building for ES2016
    Strict mode: enabled
      ✖ tsc --module 'ESNext' --experimentalDecorators --target 'ES2016' --strict main.ts
    Strict mode: disabled
      ✓ tsc --module 'ESNext' --experimentalDecorators --target 'ES2016'  main.ts
  Building for ES2017
    Strict mode: enabled
      ✖ tsc --module 'ESNext' --experimentalDecorators --target 'ES2017' --strict main.ts
    Strict mode: disabled
      ✓ tsc --module 'ESNext' --experimentalDecorators --target 'ES2017'  main.ts

实体`tsconfig`

根据这些结果，看起来好像tsconfig。

{
  "compilerOptions": {
    "target": "es5",
    "module": "<not None>",
    "experimentalDecorators": true,
    "strict": false
  }
}

最终笔记

我没有测试尽可能多的编译器选项。如果有兴趣，我可以稍后更新回购。
对于OP的问题，我仍然没有一个好的答案，这让我感到困扰。
我也检查了TS版本。 OP was using 2.4.2和I'm using 2.7.2。只是为了确保不是问题，I bumped my version down too。

Answer 2

'this'未定义，因为您没有正确配置属性描述符。

代替：

Object.defineProperty(target, key, {
      get: getter,
      set: setter,
      enumerable: true,
      configurable: true
    });

执行以下操作：

Object.defineProperty(target, key, {
      get() {
         // this is defined
      },
      set(value: any) {
         // this is defined
      },
      enumerable: true,
      configurable: true
    });

我遇到了同样的问题，上面的解决方案解决了它。

Answer 3

您可以尝试以下操作：

代替

function logProperty(target: any, key: string) {

 ...
}

使用：

const logProperty = (target: any, key: string) => {
 ...
}

因为=>的{{1}}就在外面，所以可以得到它。希望对您有所帮助！

'this'在TypeScript Property Decorator中未定义

3 个答案:

猜测

测试

`decorators.ts`

`main.ts`

`index.ts`

结果

实体`tsconfig`

最终笔记

'this'在TypeScript Property Decorator中未定义

3 个答案:

猜测

测试

decorators.ts

main.ts

index.ts

结果

实体tsconfig

最终笔记

`decorators.ts`

`main.ts`

`index.ts`

实体`tsconfig`