无法将字符串值分配给打字稿枚举（初始化程序类型的字符串不可分配给变量类型）

问题描述：

从TypeScript 2.4开始，似乎字符串枚举是一项功能。

It seems that from TypeScript 2.4 onwards String Enums are a feature.

但是以下操作无效：

enum Foo {
    A = "A",
    B = "B"
}

var foo : Foo = "A";

初始化程序类型字符串不能分配给变量类型Foo

Initializer type string not assignable to variable type Foo

字符串文字有效：

type Foo = "A" | "B";

但是如果我想要使用怎么办枚举？

答

您可以使用索引表达式来获取枚举的值：

You can use an index expression to get the value of the enum:

enum Foo {
    A = "A",
    B = "BB"
}

var foo : Foo = Foo["A"];
var fooB : Foo = Foo["B"];

请注意，键将是成员的名称而不是值。

Note that the key will be the name of the member not the value.

您也可以使用类型断言，但如果分配了错误的值，则不会出错：

You could also use a type assertion, but you will not get errors if you assign a wrong value:

var foo : Foo = "A"  as Foo;
var foo : Foo = "D"  as Foo; // No error