它跟JS是相同的语法，但它只能用在类型操作中

  1. type World = "world"
  3. type Greeting = `hello ${World}`
  5. type EmailLocaleIDs = "welcome_email" | "email_heading";
  6. type FooterLocaleIDs = "footer_title" | "footer_sendoff";
  8. type AllLocaleIDs = `${EmailLocaleIDs | FooterLocaleIDs}_id`;
  10. type AllLocaleIDs = `${EmailLocaleIDs | FooterLocaleIDs}_id`;
  11. type Lang = "en" | "ja" | "pt";
  13. type LocaleMessageIDs = `${Lang}_${AllLocaleIDs}`;
  14. // type LocaleMessageIDs = "en_welcome_email_id" | "en_email_heading_id" | "en_footer_title_id" | "en_footer_sendoff_id" | "ja_welcome_email_id" | "ja_email_heading_id" | "ja_footer_title_id" | "ja_footer_sendoff_id" | "pt_welcome_email_id" | "pt_email_heading_id" | "pt_footer_title_id" | "pt_footer_sendoff_id"
  1. type PropEventSource<Type> = {
  2.     on(eventName: `${string & keyof Type}Changed`,
  3.     callback: (newValue: any) => void): void;
  4. };
  6. declare function makeWatchedObject<Type>(obj: Type): Type & PropEventSource<Type>;
模板字面量推断
  1. type PropEventSource<Type> = {
  2.     on<Key extends string & keyof Type>
  3.         (eventName: `${Key}Changed`, callback: (newValue: Type[Key]) => void ): void;
  4. };
  7. 声明一个函数签名 返回结果 是 T 以及PropEventSource 并集结果 所以结果是有 on属性的
  8. on属性是一个 从 T中keyof得到的属性，它具有一个参数 是模板字符串 Key+Changed
  9. declare function makeWatchedObject<Type>(obj: Type): Type & PropEventSource<Type>;
  11. const person = makeWatchedObject({
  12.     firstName: "Saoirse",
  13.     lastName: "Ronan",
  14.     age: 26
  15.   });
  17. person.on("firstNameChanged", newName => {                             
  18. // (parameter) newName: string
  19. console.log(`new name is ${newName.toUpperCase()}`);
  20. });
内置字符串操作符
  1. type Greeting = "Hello, world"
  2. type ShoutyGreeting = Uppercase<Greeting>        
  3. // type ShoutyGreeting = "HELLO, WORLD"
  5. type ASCIICacheKey<Str extends string> = `ID-${Uppercase<Str>}`
  6. type MainID = ASCIICacheKey<"my_app">
  7. // type MainID = "ID-MY_APP"
  10. type Greeting = "Hello, world"
  11. type QuietGreeting = Lowercase<Greeting>       
  12. // type QuietGreeting = "hello, world"
  14. type ASCIICacheKey<Str extends string> = `id-${Lowercase<Str>}`
  15. type MainID = ASCIICacheKey<"MY_APP">    
  16. // type MainID = "id-my_app"
  18. type LowercaseGreeting = "hello, world";
  19. type Greeting = Capitalize<LowercaseGreeting>;
  20. // type Greeting = "Hello, world"
  22. type UppercaseGreeting = "HELLO WORLD";
  23. type UncomfortableGreeting = Uncapitalize<UppercaseGreeting>;           
  24. // type UncomfortableGreeting = "hELLO WORLD"