编码规范： 不要在类构造器内实例化当前对象

不要在类构造器内实例化当前对象也就是说不要将类class当做function使用

请抛弃旧有的编码习惯：

function Element (tagName, props, children) {
  if (!(this instanceof Element)) {
    if (!_.isArray(children) && children != null) {
      children = _.slice(arguments, 2).filter(_.truthy)
    }
    return new Element(tagName, props, children)
  }
   //  ......
}

我们在TS或ES6编码时会习惯性沿用ES5时代的编码习惯

export class Element implements IVNode {
  // ....
  constructor(_tagName: string);
  constructor(_tagName: string, children: any);
  constructor(_tagName: string, props: T_OBJ);
  constructor(_tagName: string, props: T_OBJ, children: T_ArrayNode);
  constructor(_tagName: string, props?: T_OBJ, children?: T_ArrayNode) {
    if (!(this instanceof Element)) {
      if (typeof props !== "undefined") {
        if (Array.isArray(children)) {
          return new Element(_tagName, props, children);
        } else {
          return new Element(_tagName, props);
        }
      } else {
        if (Array.isArray(children)) {
          return new Element(_tagName, children);
        }
      }
      return new Element(_tagName);
    }

  // ....

这种编码方式导致class , function定义不明确，职责不清晰，我们是不提倡的

推荐将实例化的代码抽离

export class Element implements IVNode {
    constructor(_tagName: string, props?: T_OBJ, children?: T_ArrayNode) {
        // ...
    }
}

export default function (_tagName: string): IVNode
export default function (_tagName: string, children: T_ArrayNode): IVNode
export default function (_tagName: string, props: T_OBJ): IVNode
export default function (_tagName: string, props: T_OBJ, children: T_ArrayNode): IVNode
export default function (_tagName: string, props?: T_OBJ, children?: T_ArrayNode): IVNode {
  if (arguments.length === 2) {
    const tmp = arguments[1]
    if (Array.isArray(tmp)) {
      return new Element(_tagName, {}, tmp)
    } else {
      return new Element(_tagName, tmp, [])
    }
  } else if (arguments.length === 1) {
    return new Element(_tagName, {}, [])
  }
  return new Element(_tagName, props, children)
}