Node.js學(xué)習(xí)之路24——Express框架的app對(duì)象

smallStone 發(fā)布于2019-08-22 14:59 / 2965人閱讀

1.express()

基于Node.js平臺(tái)，快速、開(kāi)放、極簡(jiǎn)的web開(kāi)發(fā)框架。

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

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

1.1 靜態(tài)資源管理

express.static(root, [options])

express.static,是Express內(nèi)置的唯一一個(gè)中間件.是基于serve-static開(kāi)發(fā)的,負(fù)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(duì)象是可選的,支持以下屬性

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

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

etag,Boolean類型,啟用或禁用etag生成

extensions,Mixed,設(shè)置文件擴(kuò)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(gè)目錄時(shí),重定向到尾隨/,

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

1.2. Etag

ETag是HTTP1.1中才加入的一個(gè)屬性,用來(lái)幫助服務(wù)器控制Web端的緩存驗(yàn)證.它的原理是這樣的,當(dāng)瀏覽器請(qǐng)求服務(wù)器的某項(xiàng)資源A時(shí), 服務(wù)器根據(jù)A算出一個(gè)哈希值(3f80f-1b6-3e1cb03b)并通過(guò)ETag返回給瀏覽器,瀏覽器把3f80f-1b6-3e1cb03b和A同時(shí)緩存在本地,當(dāng)下次再次向服務(wù)器請(qǐng)求A時(shí),會(huì)通過(guò)類似 If-None-Match: "3f80f-1b6-3e1cb03b"的請(qǐng)求頭把ETag發(fā)送給服務(wù)器,服務(wù)器再次計(jì)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(méi)有變化就給瀏覽器返回一個(gè)304未修改.這樣通過(guò)控制瀏覽器端的緩存,可以節(jié)省服務(wù)器的帶寬,因?yàn)榉?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(méi)有指定如何生成ETag,哈希是比較理想的選擇.

1.3. 建立基本的HTTP服務(wù)器

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

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

app.listen(3000);

1.4. app對(duì)象的locals屬性

可以在locals對(duì)象上自定義屬性

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

app.locals.email = "express@express.com";

{ 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: "express@express.com"
}

1.5. app.all(path, callback(req, res, next){...})

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

1.6. 刪除請(qǐng)求路由

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

將HTTP刪除請(qǐng)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");
});

1.7. 禁用啟用某個(gè)屬性

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

1.8. 模板引擎

app.engine(ext, callback)

根據(jù)不同的模板引擎的擴(kuò)展名,使用不同的模板

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

1.9. 設(shè)置與獲取屬性

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

1.10. get請(qǐng)求

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

將HTTP獲取請(qǐng)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");
});

1.11. 監(jiān)聽(tīng)端口

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

監(jiān)聽(tīng)端口,主機(jī),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");
    }
});

1.12. 路由參數(shù)

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(qǐng)求對(duì)象、響應(yīng)對(duì)象、下一個(gè)中間件以及該參數(shù)的值 (按該順序).如果 name 是一個(gè)數(shù)組, 則回調(diào)觸發(fā)器按聲明的順序注冊(cè)在其中聲明的每個(gè)參數(shù).此外, 對(duì)于每個(gè)已聲明的參數(shù), 除了最后一個(gè)外, 回調(diào)中的下一個(gè)調(diào)用將調(diào)用下一個(gè)聲明的參數(shù)的回調(diào).對(duì)于最后一個(gè)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(gè)中間件, 就像如果名稱只是一個(gè)字符串一樣.

參數(shù)是一個(gè)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(gè)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
*/

1.13. app.path()

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());

1.14. 模板渲染

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

回調(diào)函數(shù)返回視圖的呈現(xiàn) HTML

1.15. 路由設(shè)置

app.route(path)

返回單個(gè)路由的實(shí)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");
    });

1.16. 中間件

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(rèn)為/

路徑可以是表示路徑、路徑模式、匹配路徑的正則表達(dá)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(gè)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(huì)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");
})