示例项目

本文继续介绍“什么是 API 提取器？”页面的教程。建议从那里开始。

在本教程中，我们将考虑一个假设的 TypeScript 库项目。声明来自一个真实世界的 NPM 包 **@microsoft/sp-core-library**。它的主要入口点是 **src/index.ts**，其中包含以下导出语句

src/index.ts

export { default as Log } from './log/Log';
export { default as ILogHandler } from './log/ILogHandler';

这些定义来自三个其他源文件（为简洁起见，这里摘录了部分内容）

src/log/Log.ts

import DefaultLogHandler from './DefaultLogHandler';
import ILogHandler from './ILogHandler';

/**
 * The Log class provides static methods for logging messages at different levels (verbose,
 * info, warning, error) and with context information. Context information helps identify
 * which component generated the messages and makes the messages useful and filterable.
 * @public
 */
export default class Log {
  private static _logHandler: ILogHandler = new DefaultLogHandler();

  /**
   * Configures the logger with a different target.
   * @beta
   */
  public static initialize(logHandler: ILogHandler): void {
    Log._logHandler = logHandler;
  }

  /**
   * Logs a verbose message
   * @param   source - the source from where the message is logged, e.g., the class name.
   *          The source provides context information for the logged message.
   *          If the source's length is more than 20, only the first 20 characters are kept.
   * @param   message - the message to be logged
   *          If the message's length is more than 100, only the first 100 characters are kept.
   */
  public static verbose(source: string, message: string): void {
    this._logHandler.verbose(source, message);
  }

  . . .
  public static info(source: string, message: string): void {
    this._logHandler.info(source, message);
  }

  . . .
  public static warn(source: string, message: string): void {
    this._logHandler.warn(source, message);
  }

  . . .
  public static error(source: string, error: Error): void {
    this._logHandler.error(source, error);
  }
}

src/log/ILogHandler.ts

/**
 * The redirectable implementation for the Log class.
 * @beta
 */
export interface ILogHandler {
  verbose(source: string, message: string): void;
  info(source: string, message: string): void;
  warn(source: string, message: string): void;
  error(source: string, error: Error): void;
}

export default ILogHandler;

src/log/DefaultLogHandler.ts

（在本示例中为私有，因此其实现并不重要，留给你的想象）

让我们考察一下 API 提取器如何处理这些输入以生成 API 报告、d.ts 汇总和 API 文档输出...