基于Node.js平臺，快速、開放、極簡的web開發(fā)框架。

創(chuàng)建一個Express應(yīng)用.express()是一個由express模塊導(dǎo)出的入口top-level函數(shù).

const express = require("express");
let app = express();

express.static(root, [options])

express.static,是Express內(nèi)置的唯一一個中間件.是基于serve-static開發(fā)的,負責(zé)托管Express應(yīng)用內(nèi)的靜態(tài)資源.

root,參數(shù)指的是靜態(tài)資源文件所在的根目錄.

options,對象是可選的,支持以下屬性

dotfiles,String類型,服務(wù)dotfiles的選項.可能的值是allow,deny,ignore,默認值為ignore

maxAge,以毫秒為單位設(shè)置Cache-Control標題頭的最大屬性或ms格式的字符串,默認為0

etag,Boolean類型,啟用或禁用etag生成

extensions,Mixed,設(shè)置文件擴展

index,Boolean類型,發(fā)送目錄索引,設(shè)置false為禁用

redirect,Boolean類型,當(dāng)路徑是一個目錄時,重定向到尾隨/,

etHeaders,Function類型,設(shè)置HTTP標頭以供文件使用的函數(shù)

ETag是HTTP1.1中才加入的一個屬性,用來幫助服務(wù)器控制Web端的緩存驗證.它的原理是這樣的,當(dāng)瀏覽器請求服務(wù)器的某項資源A時, 服務(wù)器根據(jù)A算出一個哈希值(3f80f-1b6-3e1cb03b)并通過ETag返回給瀏覽器,瀏覽器把3f80f-1b6-3e1cb03b和A同時緩存在本地,當(dāng)下次再次向服務(wù)器請求A時,會通過類似 If-None-Match: "3f80f-1b6-3e1cb03b"的請求頭把ETag發(fā)送給服務(wù)器,服務(wù)器再次計算A的哈希值并和瀏覽器返回的值做比較,如果發(fā)現(xiàn)A發(fā)生了變化就把A返回給瀏覽器200,如果發(fā)現(xiàn)A沒有變化就給瀏覽器返回一個304未修改.這樣通過控制瀏覽器端的緩存,可以節(jié)省服務(wù)器的帶寬,因為服務(wù)器不需要每次都把全量數(shù)據(jù)返回給客戶端.
注：HTTP中并沒有指定如何生成ETag,哈希是比較理想的選擇.

const express = require("express");
let app = express();

app.get("/", (req, res) => {
    res.send("hello world");
});

app.listen(3000);

可以在locals對象上自定義屬性

app.locals.title = "my express title";

app.locals.email = "[email protected]";

{ settings: { 
    "x-powered-by": true,
     etag: "weak",
     "etag fn": [Function: wetag],
     env: "development",
     "query parser": "extended",
     "query parser fn": [Function: parseExtendedQueryString],
     "subdomain offset": 2,
     "trust proxy": false,
     "trust proxy fn": [Function: trustNone],
     view: [Function: View],
     views: "E:Selfpointviews",
     "jsonp callback name": "callback" 
    },
    title: "my express title",
    email: "[email protected]"
}

app.all("*", fn1, fn2...)
// 等價于
app.all("*", fn1)
app.all("*", fn2)

app.delete(path, callback [, callback ...])

將HTTP刪除請求路由到具有指定回調(diào)函數(shù)的指定路徑

app.delete("/", function (req, res) {
    res.send("DELETE request to homepage");
});

禁用app.disable(name),app.disabled(name)

啟用app.able(name),app.abled(name)

app.set("username", "express server");
console.log(app.get("username")); //express server

app.set("username", "express server");
app.disable("username");
console.log(app.get("username")); //false

app.engine(ext, callback)

根據(jù)不同的模板引擎的擴展名,使用不同的模板

app.engine("jade", require("jade").__express);
app.engine("html", require("ejs").renderFile);

app.set("title", "text");
console.log(app.get("title")); // text

app.get(path, callback [, callback ...])

將HTTP獲取請求路由到具有指定回調(diào)函數(shù)的指定路徑

app.get("/", function (req, res) {
    res.send("GET request to homepage");
});

app.listen(port, [hostname], [backlog], [callback(err)])

監(jiān)聽端口,主機,最大連接數(shù)量,回調(diào)函數(shù)

const express = require("express");
let app = express();

app.get("/", function (req, res) {
    res.send("home page");
});

app.listen(3000, "localhost", 100, function (err) {
    if (err) {
        console.log("error");
    } else {
        console.log("the http server is running at localhost:3333");
    }
});

app.param([name],callback(req, res, next, id){...})

將回調(diào)觸發(fā)器添加到路由參數(shù), 其中名稱是參數(shù)的名稱或它們的數(shù)組, 函數(shù)是回調(diào)函數(shù).回調(diào)函數(shù)的參數(shù)是請求對象、響應(yīng)對象、下一個中間件以及該參數(shù)的值 (按該順序).
如果 name 是一個數(shù)組, 則回調(diào)觸發(fā)器按聲明的順序注冊在其中聲明的每個參數(shù).此外, 對于每個已聲明的參數(shù), 除了最后一個外, 回調(diào)中的下一個調(diào)用將調(diào)用下一個聲明的參數(shù)的回調(diào).對于最后一個參數(shù), 調(diào)用 next 將調(diào)用當(dāng)前正在處理的路由的下一個中間件, 就像如果名稱只是一個字符串一樣.

參數(shù)是一個字符串

app.param("id", (req, res, next, id) => {
    console.log("called only once");
    next();
});

app.get("/user/:id", (req, res, next) => {
    console.log("although this matches");
    next();
});

app.get("/user/:id", (req, res) => {
    console.log("this matches too");
    res.send("end user id");
});
/**
called only once
although this matches
this matches too
*/

參數(shù)是一個數(shù)組

app.param(["id", "page"], (req, res, next, id) => {
    console.log("called only once", id);
    next();
});

app.get("/user/:id/:page", (req, res, next) => {
    console.log("although this matches");
    next();
});

app.get("/user/:id/:page", (req, res) => {
    console.log("this matches too");
    res.send("end user id");
});
/**
called only once kkk
called only once 555
although this matches
this matches too
*/

返回應(yīng)用程序的規(guī)范化路徑

let express = require("express");
let app = express();
let blog = express();
let blogAdmin = express();

app.use("/blog", blog);
blog.use("/admin", blogAdmin);

console.log(app.path());
console.log(blog.path());
console.log(blogAdmin.path());

app.render(view, [locals], callback(err,html){...})

回調(diào)函數(shù)返回視圖的呈現(xiàn) HTML

app.route(path)

返回單個路由的實例

app.route("/one")
    .all(function (req, res, next) {
        console.log("route all");
        next();
    })
    .get(function (req, res, next) {
        res.json({
            code: 2589,
            msg: "route get msg"
        });
    })
    .post(function (req, res, next) {
        res.send("this is route post send msg");
    });

app.use([path,] callback(req, res, next){...})

在路徑上裝載中間件函數(shù).如果未指定路徑, 則默認為/

路徑可以是表示路徑、路徑模式、匹配路徑的正則表達式或其組合數(shù)組的字符串

app.use()中間件可以使用正則匹配路徑,可以有多個中間件函數(shù)

可使用的地方

app.use(express.static(__dirname + "/public"));
app.use("/static", express.static(__dirname + "/public"));
app.use(express.static(__dirname + "/public"));
app.use(logger());
app.use(express.static(__dirname + "/public"));
app.use(express.static(__dirname + "/files"));
app.use(express.static(__dirname + "/uploads"));

中間件示例

app.use("/user/person", (req, res, next) => {
    console.log(req.originalUrl); // /user/person
    console.log(req.baseUrl); // /user/person
    console.log(req.path); // /
    next();
});

如果使用了app.use(callback()),就不會觸發(fā)app.get("/", callback())

// this middleware will not allow the request to go beyond it
app.use((req, res, next) => {
    res.send("Hello World");
})

// requests will never reach this route
app.get("/", (req, res) => {
    res.send("Welcome");
})