koa加载解析记录

> 因项目需要使用koa模拟服务器返回接口，研究下koa加载过程

1、nodejs下的require, 一切node模块的加载都是从node_modules开始的，打开koa模块package.json ，仅关注入口main属性对应的启动项，和dependencies 属性的依赖项，npm模块的依赖会检查如果dependencies下对应的文件是否存在，如果不存在则加载，参考朴灵深入浅出nodejs

 {
  "main": "lib/application.js",
  "dependencies": {
    "accepts": "^1.3.5",
    "cache-content-type": "^1.0.0",
    "content-disposition": "~0.5.2",
    "content-type": "^1.0.4",
    "cookies": "~0.7.1",
    "debug": "^3.1.0",
    "delegates": "^1.0.0",
    "depd": "^1.1.2",
    "destroy": "^1.0.4",
    "error-inject": "^1.0.0",
    "escape-html": "^1.0.3",
    "fresh": "~0.5.2",
    "http-assert": "^1.3.0",
    "http-errors": "^1.6.3",
    "is-generator-function": "^1.0.7",
    "koa-compose": "^4.1.0",
    "koa-convert": "^1.2.0",
    "koa-is-json": "^1.0.0",
    "on-finished": "^2.3.0",
    "only": "~0.0.2",
    "parseurl": "^1.3.2",
    "statuses": "^1.5.0",
    "type-is": "^1.6.16",
    "vary": "^1.1.2"
  },
  "devDependencies": {
    "eslint": "^3.17.1",
    "eslint-config-koa": "^2.0.0",
    "eslint-config-standard": "^7.0.1",
    "eslint-plugin-promise": "^3.5.0",
    "eslint-plugin-standard": "^2.1.1",
    "jest": "^20.0.0",
    "supertest": "^3.1.0"
  }
}

2、app.use 中间件, 其实就是做了个记录，把传入会掉push到middleware，callback函数会在http.createServer中以高阶函数的形式返回，注入ctx和之前push到middleware中的回调。所以当改变url触发了http.createServer ，会执行use中的函数。

//中间件  
use(fn) {
    if (typeof fn !== 'function') throw new TypeError('middleware must be a function!');
    if (isGeneratorFunction(fn)) {
      deprecate('Support for generators will be removed in v3. ' +
                'See the documentation for examples of how to convert old middleware ' +
                'https://github.com/koajs/koa/blob/master/docs/migration.md');
      fn = convert(fn);
    }
    debug('use %s', fn._name || fn.name || '-');
    this.middleware.push(fn);
    return this;
  }
//监听
  listen(...args) {
    debug('listen');
    const server = http.createServer(this.callback());
    return server.listen(...args);
  }
//监听回调
 callback() {
    const fn = compose(this.middleware);

    if (!this.listenerCount('error')) this.on('error', this.onerror);

    const handleRequest = (req, res) => {
      const ctx = this.createContext(req, res);
      return this.handleRequest(ctx, fn);
    };

    return handleRequest;
  }

3、自己开发use

//class router
let data = {}
class router {
  
  constructor(str,fun){
    Object.defineProperty(router,"data",{value:{}})
  }
   get(str,fun){
    router.data[str] = fun;
   }
   async main(params,next){  
        await next();
       let reg = /\/.*/g;
       let {path} = params;
       router.data[path](params);
    }

}
module.exports=new router;

//执行

const Koa = require('koa');
const app = new Koa();
const router = require("./router");
router.get("/getData",async arg=>{
    
    arg.body="hello world"
})
app.use(router.main); //响应
app.listen(3000);