TypeScript enum 反向映射 / 双向映射 All In One

TypeScript enum 反向映射 / 双向映射 All In One

TypeScript enum 枚举实现原理

JS enum

enum Direction {
  Up,
  Down,
  Left,
  Right
}

// js
var Direction;
(function (Direction) {
    Direction[Direction["Up"] = 0] = "Up";
    Direction[Direction["Down"] = 1] = "Down";
    Direction[Direction["Left"] = 2] = "Left";
    Direction[Direction["Right"] = 3] = "Right";
})(Direction || (Direction = {}));

// 等价于
function enum_generator(arr = []) {
  let result = {};
  for(const [i, item] of arr.entries()) {
    // console.log(`i, item`, i, item)
    result[result[item] = i] = item;
  }
  return result;
}

const Directions = enum_generator(["Up","Down","Left","Right"]);

// 利用了js 对象赋值的返回值就是所赋值的特性
obj = {};
{}
obj['Up'] = 0;
// 0
obj[0] = "Up";
// 'Up'

TypeScript enum

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

demos

https://www.typescriptlang.org/play

enum Direction {
  Up = 'UP',
  Down = 3,
  Left = 5,
  Right = 7,
}
// key & index

"use strict";
var Direction;
(function (Direction) {
    Direction["Up"] = "UP";
    Direction[Direction["Down"] = 3] = "Down";
    Direction[Direction["Left"] = 5] = "Left";
    Direction[Direction["Right"] = 7] = "Right";
})(Direction || (Direction = {}));
// key & index

推荐全部使用 key & index 一一双向映射， 防止出现 index 可能不存在问题；

https://www.typescriptlang.org/play?ssl=7&ssc=15&pln=1&pc=1#code/KYOwrgtgBAIglgJ2AYwC5wPYigbwFBRQCqADlALxQDkRAClQDQGwYDu2lAzE4QDLAAzVBSgBWHlABKcAOYALYZQDsTAL54A9BqgBrYAE8oAMihwQAE2AAPIA

refs

https://www.cnblogs.com/xgqfrms/p/13881723.html

---

---

©xgqfrms 2012-2020

www.cnblogs.com/xgqfrms 发布文章使用：只允许注册用户才可以访问！

原创文章，版权所有©️xgqfrms, 禁止转载 🈲️，侵权必究⚠️！

---