TypeScript里实现函数重载

在 TypeScript 中，函数重载允许你为一个函数提供多个函数简要。通过函数重载，你可以实现在同一函数名下支持多种参数和返回值类型。这里我们将通过两个示例来认识 TypeScript 中函数重载的使用方式和最佳实践。

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示例一：在类中实现函数重载

export class BookService {
  /**
   * get book by id
   * @param id book id
   * @returns book
   */
  getBook(id: string): Book;

  /**
   * get book by condition
   * @param condition book condition
   * @returns book list
   */
  getBook(condition: { title?: string; publishTime?: Date }): Book[];

  public getBook(condition: string | { title?: string; publishTime?: Date }): Book | Book[] {
    if (typeof condition === 'string') {
      // logic to get book by id
      return {} as Book;
    }
    // logic to get book by condition
    return [{} as Book];
  }
}

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示例二：在普通函数中使用函数重载

/**
 * get book by id
 * @param id book id
 * @returns book
 */
export function getBook(id: string): Book;

/**
 * get book by condition
 * @param condition book condition
 * @returns book list
 */
export function getBook(condition: { title?: string; publishTime?: Date }): Book[];

export function getBook(condition: string | { title?: string; publishTime?: Date }): Book | Book[] {
  if (typeof condition === 'string') {
    // logic to get book by id
    return {} as Book;
  }
  // logic to get book by condition
  return [{} as Book];
}

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总结

在 TypeScript 中，函数重载是一种很有用的功能，适合解决同一作用下的不同场景。根据实际需求，你可以在类中或选择单独函数重载方式，以更好地符合项目策略。