我在TypeScript中定义了以下enum:
enum Color{
Red, Green
}
现在在我的函数中,我以字符串的形式接收颜色。我尝试了以下代码:
var green= "Green";
var color : Color = <Color>green; // Error: can't convert string to enum
如何将该值转换为enum?
我在TypeScript中定义了以下enum:
enum Color{
Red, Green
}
现在在我的函数中,我以字符串的形式接收颜色。我尝试了以下代码:
var green= "Green";
var color : Color = <Color>green; // Error: can't convert string to enum
如何将该值转换为enum?
当前回答
其他的变化可以是
const green= "Green";
const color : Color = Color[green] as Color;
其他回答
以这种方式创建的枚举被编译成一个对象,该对象同时存储正向(名称->值)和反向(值->名称)映射。从这张chrome devtools截图中我们可以看到:
下面是一个关于对偶映射如何工作以及如何从一个映射转换到另一个映射的例子:
enum Color{
Red, Green
}
// To Number
var greenNr: number = Color['Green'];
console.log(greenNr); // logs 1
// To String
var greenString: string = Color[Color['Green']]; // or Color[Color[1]
console.log(greenString); // logs Green
// In your example
// recieve as Color.green instead of the string green
var green: string = Color[Color.Green];
// obtain the enum number value which corresponds to the Color.green property
var color: Color = (<any>Color)[green];
console.log(color); // logs 1
从Typescript 2.1开始,enum中的字符串键都是强类型的。Keyof typeof用于获取可用字符串键的信息(1):
enum Color{
Red, Green
}
let typedColor: Color = Color.Green;
let typedColorString: keyof typeof Color = "Green";
// Error "Black is not assignable ..." (indexing using Color["Black"] will return undefined runtime)
typedColorString = "Black";
// Error "Type 'string' is not assignable ..." (indexing works runtime)
let letColorString = "Red";
typedColorString = letColorString;
// Works fine
typedColorString = "Red";
// Works fine
const constColorString = "Red";
typedColorString = constColorString
// Works fine (thanks @SergeyT)
let letColorString = "Red";
typedColorString = letColorString as keyof typeof Color;
typedColor = Color[typedColorString];
https://www.typescriptlang.org/docs/handbook/advanced-types.html#index-types
对于Typescript >= 4,此代码工作:
enum Color{
Red, Green
}
// Conversion :
var green= "Green";
var color : Color = green as unknown as Color;
enum Color{
Red, Green
}
// To String
var green: string = Color[Color.Green];
// To Enum / number
var color : Color = Color[green as keyof typeof Color]; //Works with --noImplicitAny
这个例子使用TypeScript中的——noImplicitAny
来源: https://github.com/Microsoft/TypeScript/issues/13775 issuecomment - 276381229 https://www.typescriptlang.org/docs/handbook/advanced-types.html索引类型中
如果您为枚举提供字符串值,则直接强制转换可以很好地工作。
enum Color {
Green = "Green",
Red = "Red"
}
const color = "Green";
const colorEnum = color as Color;