Question

public testOptions: "Undecided" | "Yes" | "No" = "Undecided";

这段代码的含义是什么意思？
什么是变量testOptions的类型？
testOptions是数组，字符串还是其他东西？
“不”=“未定”是什么意思？
管道符号“|”是什么意思？

Answer 1

使用管道符号|分隔的类型称为联合类型，可以作为OR操作读取。此案例中的=符号表示作业。含义属性testOptions具有默认值"Undecided"

您的代码可以重写为：

// Foo is of type string, but not just any string, only the literal values
// "Undecided", "Yes", or "No". Any other string won't match the type.
type Foo = "Undecided" | "Yes" | "No";

// Will error because "bar" is not one of "Undecided", "Yes", or "No"
const a: Foo = "bar";

// Will work
const b: Foo = "Undecided";

要详细了解TypeScript中的高级类型，我强烈推荐docs on advanced types

Answer 2

在打字稿中，变量类型定义为variableName: type。

类型可以是任何东西。

原始值：字符串，数字
复杂值：MyClass1，IInterface1

还有一个联合运算符（|），用于合并多种类型。

因此，如果您有一个可以包含数字或字符串的变量，那么它将被定义为variable: number | string。

现在如果你想拥有一个只能在特定类型中拥有特定值的变量呢？

public testOptions：＆＃34; Undecided＆＃34; | ＆＃34;是＆＃34; | ＆＃34;否＆＃34; =＆＃34;未定＆＃34 ;;

现在，您的testOptions可以"Undecided" | "Yes" | "No"，您可以将其默认设置为"Undecided"

Answer 3

public testOptions: "Undecided" | "Yes" | "No" = "Undecided";

您已定义了一个字符串变量。
字符串，但是"Undecided" | "Yes" | "No"

如果更改值

public testOptions: "Undecided" | "Yes" | "No" = "decided";

它会抛出错误，因为它是字符串但它应该超出"Undecided" | "Yes" | "No"

这段代码创建了一个新类型，就像string，objject，number;此代码创建了一个用户定义的类型

type UndecideYesNoType = "Undecided" | "Yes" | "No";

Answer 4

它就像一个缺少enum ......

以下将编译：

testOptions: "Undecided" | "Yes" | "No" = "Undecided";
testOptions: "Undecided" | "Yes" | "No" = "Yes";
testOptions: "Undecided" | "Yes" | "No" = "No";
testOptions: "a" | "b" | "c" = "a";

这不会编译：

testOptions: "Undecided" | "Yes" | "No" = "xxx";
testOptions: "a" | "b" | "c" = "xxx";

因为＆＃34; xxx＆＃34;在高级类型声明中不存在。

与枚举相反：

enum MyEnum{
    Undecided= 1,
    Yes,
    No
}
testOptions:MyEnum = MyEnum.Yes; <-- so much easier to understand

打字稿中这段代码的含义是什么？ public testOptions：“未定”| “是的”| “不”=“未定”;

4 个答案: