Typescript：如何使用默认 getter 显示类的属性

Question

我有一个接口和一个类如下

export interface ISample {
  propA: string;
  propB: string;
}

export class Sample {
  
  private props = {} as ISample;

  public get propA(): string {
    return this.props.propA;
  }

  public set propA(propA: string) {
    this.props.propA = propA;
  }

  public get propB(): string {
    return this.props.propB;
  }

  public set propB(propB: string) {
    this.props.propB = propB;
  }

}

在我的代码中，我使用类来初始化对象，如下所示。

let sample = new Sample();
sample.propA = 'A';
sample.propB = 'B';

但是当我尝试使用console.log(sample) 打印对象时，我得到了

props: {propsA: "A", propsB: "B"}
propsA: (...)
propsB: (...)

当我使用console.log(sample) 时，如何让输出仅显示{propsA: "A", propsB: "B"}？

PS：我正在使用typescript 3.8.3 和Angular 9。

Answer 1

您的类Sample 有一个名为sample 的类属性，它继承ISample。那就是说很明显你得到了props: { propA: "A", propB: "B"}的日志。

如果您希望propA 和propB 成为您的类的直接元素，您必须正确继承接口。这样做，您必须将propA 和propB 设置为Sample 的直接元素，这会导致您想要的日志。

export class Sample implements ISample {
  propsA = '';
  propsB = '';
}

请记住，只要您使用 private 状态，就必须相应地调整您的 setter 和 getter。

Answer 2

您可以覆盖 toString() 方法：

export interface ISample {
  propA: string;
  propB: string;
}

export class Sample {
  
  props = {} as ISample;

  public get propA(): string {
    return this.props.propA;
  }

  public set propA(propA: string) {
    this.props.propA = propA;
  }

  public get propB(): string {
    return this.props.propB;
  }

  public set propB(propB: string) {
    this.props.propB = propB;
  }

  toString() {
    return this.props;
  }
}

let sample = new Sample();
sample.propA = 'A';
sample.propB = 'B';

console.log(sample.props)

Answer 3

看到您希望直接使用属性而不需要任何类对象实例，您可以完全跳过Sample 类。相反，您可以尝试直接使用ISample 接口。

试试下面的

export interface ISample {
  propA: string;
  propB: string;
}

export class AppComponent  {
  sample = {} as ISample;

  ngOnInit() {
    this.sample.propA = 'A';
    this.sample.propB = 'B';

    // prints {propA: "A", propB: "B"}
    console.log(this.sample);
  }
}

Answer 4

您几乎无法通过console.log 更改类的显示。此功能在浏览器中实现，几乎没有任何操作空间。例如implementation in FF

function log(aThing) {
  if (aThing === null) {
    return "null\n";
  }

  if (aThing === undefined) {
    return "undefined\n";
  }

  if (typeof aThing == "object") {
    let reply = "";
    let type = getCtorName(aThing);
    if (type == "Map") {
      reply += "Map\n";
      for (let [key, value] of aThing) {
        reply += logProperty(key, value);
      }
    }
    else if (type == "Set") {
      let i = 0;
      reply += "Set\n";
      for (let value of aThing) {
        reply += logProperty('' + i, value);
        i++;
      }
    }
    else if (type.match("Error$") ||
             (typeof aThing.name == "string" &&
              aThing.name.match("NS_ERROR_"))) {
      reply += "  Message: " + aThing + "\n";
      if (aThing.stack) {
        reply += "  Stack:\n";
        var frame = aThing.stack;
        while (frame) {
          reply += "    " + frame + "\n";
          frame = frame.caller;
        }
      }
    }
    else if (aThing instanceof Components.interfaces.nsIDOMNode && aThing.tagName) {
      reply += "  " + debugElement(aThing) + "\n";
    }
    else {
      let keys = Object.getOwnPropertyNames(aThing);
      if (keys.length > 0) {
        reply += type + "\n";
        keys.forEach(function(aProp) {
          reply += logProperty(aProp, aThing[aProp]);
        });
      }
      else {
        reply += type + "\n";
        let root = aThing;
        let logged = [];
        while (root != null) {
          let properties = Object.keys(root);
          properties.sort();
          properties.forEach(function(property) {
            if (!(property in logged)) {
              logged[property] = property;
              reply += logProperty(property, aThing[property]);
            }
          });

          root = Object.getPrototypeOf(root);
          if (root != null) {
            reply += '  - prototype ' + getCtorName(root) + '\n';
          }
        }
      }
    }

    return reply;
  }

  return "  " + aThing.toString() + "\n";
}

如您所见，对于类实例 (typeof aThing == "object")，它调用 Object.getOwnPropertyNames 并显示每个属性。

请注意，toString 无济于事 - 它不用于对象（typeof aThing == "object"）

同样，V8ValueStringBuilder.append 在 Chrome 中

if (value->IsObject() && !value->IsDate() && !value->IsFunction() &&
        !value->IsNativeError() && !value->IsRegExp()) {
    v8::Local<v8::Object> object = v8::Local<v8::Object>::Cast(value);
    v8::Local<v8::String> stringValue;
    if (object->ObjectProtoToString(m_context).ToLocal(&stringValue))
        return append(stringValue);
}

/**
  * Call builtin Object.prototype.toString on this object.
  * This is different from Value::ToString() that may call
  * user-defined toString function. This one does not.
  */
 V8_WARN_UNUSED_RESULT MaybeLocal<String> ObjectProtoToString(
     Local<Context> context);

另见：Does console.log invokes toString method of an object?