這在React代碼庫中有什么作用？

Question

我在React代碼庫中看到以下內容：

export type TypeOfWork = 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10;

到底在做什么

來源： https : //github.com/facebook/react/blob/master/src/shared/ReactTypeOfWork.js

Answer 1

這是流程或打字稿語法。

它定義了一個自定義類型，只能是0到10之間的數字。

export type TypeOfWork = 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10;
let x: TypeOfWork = 0;

x = 12; // <-- compiler would throw an error here

在這種情況下，枚舉可能更好（僅適用於打字稿）

https://www.typescriptlang.org/docs/handbook/enums.html

export const enum TypeOfWork {
  IndeterminateComponent = 0, // Before we know whether it is functional or class
  FunctionalComponent = 1,
  ClassComponent = 2,
  HostRoot = 3, // Root of a host tree. Could be nested inside another node.
  HostPortal = 4, // A subtree. Could be an entry point to a different renderer.
  HostComponent = 5,
  HostText = 6,
  CoroutineComponent = 7,
  CoroutineHandlerPhase = 8,
  YieldComponent = 9,
  Fragment = 10
};

如您在編譯視圖中所見，這將被更好地縮小