对象变量未在方法内更新

Question

我正在尝试更新作为参数传递给打字稿代码中方法的对象，但它从未改变：

export class MyClass {

  //...
  myMethod(array) {
    //...
    let myVariable: MyObject;
    array.forEach(currentElement => {
      if (someCondition) {
        this.replaceVariable(myVariable, currentElement);
      }
    });

    console.log(myVariable); // myVariable here is Undefined

    return myVariable;
  }

  private replaceVariable(variableToReplace: MyObject, newValue: MyObject) {
    if (variableToReplace == null) {
      variableToReplace = newValue;
    } else {
      if (someCondition) {
        variableToReplace = newValue;
      }
    }

    console.log(variableToReplace); // variableToReplace here is replaced by newValue
  }
}

由于对象总是通过引用传递，所以我期望 myVariable 在调用方法 replaceVariable 后获得新值。但是正如您在代码注释中看到的那样，变量在 replaceVariable 方法内部被替换，并在 myMethod

中保留一个 undefined 值

Answer 1

As objects are always passed by reference, I was expecting that myVariable gets the new value after calling the method replaceVariable

是的，它们是通过引用传递的。然而，它们 not 作为 out 变量传递。你可以改变，但你不能重新分配。

差异

由于 JavaScript 不支持 out 变量，这里是两者的 C# 参考，以便您了解差异：

对象变量未在方法内更新

Object variable isn't updated inside a method

pass-by-reference

typescript

差异