nodejs 如何在 Express.js 中跳过一个中间件？

如何在 Express.js 中跳过一个中间件？

原文:https://www . geeksforgeeks . org/如何跳过中间件 in-express-js/

如果我们想跳过一个中间件，我们可以将参数传递给中间件函数，并根据该参数决定调用哪个中间件和不调用哪个中间件。

先决条件:

express.js: 处理路由。

设置环境和执行:

步骤 1: 初始化节点项目

js npm init
步骤 2: 安装所需模块

js npm install express

示例:

index.js

const express = require("express");
// const database = require('./sqlConnection');

const app = express();

// Start server on port 5000
app.listen(5000, () => {
  console.log(`Server is up and running on 5000 ...`);
});

// define middleware 1
let middleware1 = (req, res, next) => {

    // decide a parameter
    req.shouldRunMiddleware2 = false;

    console.log("Middleware 1 is running !");
    next();
}

// define middleware 2
let middleware2 = (req, res, next) => {
    if(!req.shouldRunMiddleware2) {
        console.log("Skipped middleware 2");
        return next();
    }

    console.log("Middleware 2 is running !");
}

// define middleware 3
let middleware3 = (req, res, next) => {
    console.log("Middleware 3 is running !");
}

// create route for home page '/'
app.get("/", middleware1, middleware2, middleware3);

输出:运行以下命令启动服务器。之后转到浏览器上的http://localhost:5000查看控制台中的输出