http://www.liaoxuefeng.com/wiki/001434446689867b27157e896e74d51a89c25cc8b43bdb3000/001471133885340dad9058705804899b1cc2d0a10e7dc80000

for..of for..in 區別

簡單說，for in是遍歷鍵名，for of是遍歷鍵值。例如：

let arr = ["a","b"];
for (a in arr) {
    console.log(a);//1,2
}

for (a of arr) {
    console.log(a);//a,b
}

const var let 區別

const定義的變量不可以修改，而且必須初始化.

var定義的變量可以修改，如果不初始化會輸出undefined，不會報錯。

let是塊級作用域，函數內部使用let定義后，對函數外部無影響。

Paste_Image.png

index.js

var fn_index = async (ctx, next) => {
    ctx.response.body = `<h1>Index</h1>
        <form action="/signin" method="post">
            <p>Name: <input name="name" value="koa"></p>
            <p>Password: <input name="password" type="password"></p>
            <p><input type="submit" value="Submit"></p>
        </form>`;
};

var fn_signin = async (ctx, next) => {
    var name = ctx.request.body.name || '',
        password = ctx.request.body.password || '';
    console.log(`signin with name: ${name},password: ${password}`);
    if (name === 'koa' && password === '12345') {
        ctx.response.body = `<h1>Welcome, ${name}</h1>`;
    } else {
        ctx.response.body = `<h1>Login failed!</h1>
                <p><a href='/'>Try again</a><p>`;
    }
};

module.exports = {
    'GET /': fn_index,
    'POST /signin': fn_signin
};

hello.js

var fn_hello = async (ctx, next) => {
    var name = ctx.params.name;
    ctx.response.body = `<h1>Hello,${name}!</h1>`;
};

module.exports = {
    'GET /hello/:name': fn_hello
}

app.js

'use strict';

const fs = require('fs');
const Koa = require('koa');
const router = require('koa-router')();
const bodyParser=require('koa-bodyparser');
const app = new Koa();


var files = fs.readdirSync(__dirname + '/controllers');

console.log('__dirname/controllers:  '+__dirname+'/controllers');

var js_files = files.filter((f) => {
    return f.endsWith('.js');
});

for (var f of js_files) {
    console.log(`process controller: ${f}...`);

    let mapping = require(__dirname + '/controllers/' + f);
    for (var url in mapping) {
        console.log('url----------'+url);
        if (url.startsWith('GET ')) {
            var path = url.substring(4);
            console.log('path--------'+path);
              console.log('mapping[url]--------'+mapping[url]);
            router.get(path, mapping[url]);
            console.log(`register URL mapping: GET ${path}`);
        } else if (url.startsWith('POST')) {
            var path = url.substring(5);
            router.post(path, mapping[url]);
            console.log(`register URL mapping: POST ${path}`);
        } else {
            console.log(`invalid URL :${url}`);
        }
    }
}

app.use(bodyParser());
app.use(router.routes());
app.listen(3000);

console.log(`app started at port 3000`);

package.json

 {
    "name": "hello-koa2",
    "version": "1.0.0",
    "description": "Hello Koa 2 example with async",
    "main": "app.js",
    "scripts": {
        "start": "node app.js"
    },
    "keywords": [
        "koa",
        "async"
    ],
    "author": "Michael Liao",
    "license": "Apache-2.0",
    "repository": {
        "type": "git",
        "url": "https://github.com/michaelliao/learn-javascript.git"
    },
    "dependencies": {
        "koa": "2.0.0",
        "koa-router": "7.0.0",
        "koa-bodyparser": "3.2.0"
    }
}

記得npm install