函数也有类型，函数的类型声明像箭头函数
image.png

在对象中声明函数类型

  1. type Query = {
  2.     query: string,
  3.     tags?: string[],
  4.     assemble: (includeTags: boolean) => string
  5. }
  7. const query: Query = {
  8.     query: 'Ember',
  9.      tags: ['javascript'],
  10.      assemble(includeTags = false) {
  11.          let query = `?query=${this.query}`
  12.          if(includeTags && typeof this.tags !== 'undefined') {
  13.              query += `&${this.tags.join(',')}`
  14.          }
  15.          return query
  16.      }
  17. }

类型可以组合

  1. type AssembleFn = (includeTags: boolean) => string
  2. type Query = {
  3.     query: string,
  4.     tags?: string[],
  5.     assemble: AssembleFn
  6. }

函数中的函数类型

  1. type SearchFn = (
  2.     query: string, tags?: string[] | undefined
  3. ) => Promise<Result[]>
  5. declare function displaySearch(
  6.     inputId: string,
  7.     outputId: string,
  8.     search: SearchFn
  9. ): void

当我们不想return 任何值时，函数返回值类型用 void

传递匿名函数

  1. displaySearch(
  2.     'searchField',
  3.     'result',
  4.     function(query, tags) {
  5.         return Promise.resolve([{
  6.             title: `the ${query} test book`,
  7.             url: `/${query}-design-patterns`,
  8.             abstract:  `A practical book on ${query}`
  9.         }])
  10.     }
  11. )

相同类型的函数的参数名并不需要和声明的相同，只要顺序相同就行
例如下面用term替代query, 去掉tags

  1. const testSearch: SearchFn = function(term) {
  2.     // All types still intact
  3.   return Promise.resolve([{
  4.     title: `The ${term} test book`,
  5.     url: `/${term}-design-patterns`,
  6.     abstract: `A practical book on ${term}`
  7.   }])
  8. }