将 null 分配给类型化变量时，Visual Studio Code 在 Typescript 代码中报告错误

Question

I have the following interface:

interface CompositeNodeInterface {
  name: string;
  definer: any;
  parent: CompositeNodeInterface;
  children: [CompositeNodeInterface];

  addChild(definer: any): CompositeNodeInterface
}

As you can see, attribute parent is typed as an object that recursively implements the same interface, and attribute children is typed as an array of objects that equally implement recursively the same interface.

I have the following class that implements CompositeNodeInterface :

export default class CompositeNode implements CompositeNodeInterface {
  name: string;
  definer: any;
  parent: CompositeNode;
  children: [CompositeNode];

  constructor(definer: any) {
    switch(definer.constructor.name) {
      case 'Object':
        if ('name' in definer) {
          this.name = definer.name;
        } else {
          this.name = String(Object.values(definer)[0]);
        }

        break;
      default:
        this.name = definer.toString();
    }

    this.definer = definer;
    this.parent = null;
    this.children = [];
  }

  acceptVisit(visitor: VisitorInterface) {
    return visitor.visit(this)
  }
}

The problem is that when attribute parent is set to null , VSC reports the following error: Type 'null' is not assignable to type 'CompositeNode' , and when attribute children is set to [] , VSC reports Type '[]' is not assignable to type '[CompositeNode]' .

I read here that all attributes are nullable, so I would expect these operations to be valid.

Answer 1

you no longer can assign null or undefined values to every field since: https://github.com/Microsoft/TypeScript/pull/7140

you need to explicitly set the value to nullable, possibly using of a union type, such as CompositeNode | null CompositeNode | null , or additionally you could make parent optional