在打字稿的枚举中使用字符串变量

Question

在打字稿中是否可以在枚举中使用字符串变量？我可以像这样在枚举中使用字符串：

enum AllDirections {
  TOP = 'top',
  BOTTOM = 'bottom',
  LEFT = 'left',
  RIGHT = 'right',
}

但是这段代码：

const top: string = 'top'
const bottom: string = 'bottom'
const left: string = 'left'
const right: string = 'right'

enum AllDirections {
  TOP = top,
  BOTTOM = bottom,
  LEFT = left,
  RIGHT = right,
}

结果有错误：Type 'string' is not assignable to type 'AllDirections'

Answer 1

如果您确实想这样做，那么您可以将这些值断言为any：

enum AllDirections {
  TOP = top as any,
  BOTTOM = bottom as any,
  LEFT = left as any,
  RIGHT = right as any
}

这样做的问题是，如果您将它们分配给字符串值，那么它将需要对字符串进行断言。这并不理想：

let str: string = AllDirections.TOP as any as string;

或者，它有点冗长，但如果您希望成员具有正确的类型，您可以考虑使用对象：

// remove the explicit string types so that these are typed
// as their string literal values
const top = 'top';
const bottom = 'bottom';
const left = 'left';
const right = 'right';

type AllDirections = Readonly<{
    TOP: typeof top,
    BOTTOM: typeof bottom,
    LEFT: typeof left,
    RIGHT: typeof right
}>; 

const AllDirections: AllDirections = {
    TOP: top,
    BOTTOM: bottom,
    LEFT: left,
    RIGHT: right
};

另一种选择是翻转字符串的存储位置：

 enum AllDirections {
    TOP = 'top',
    BOTTOM = 'bottom',
    LEFT = 'left',
    RIGHT = 'right',
}

const top = AllDirections.TOP;
const bottom = AllDirections.BOTTOM;
const left = AllDirections.LEFT;
const right = AllDirections.RIGHT;