表示当浏览器发出请求时两次调用的中间件函数 [英] express middleware functions invoked twice when request is made from browser

问题描述

下面是我的nodejs代码

Below is my nodejs code

const express = require('express');

const app = express();

app.use('/', (req, res, next) => {
    console.log("In interceptor");
    next();
});

app.use('/users', (req, res, next) => {
    console.log('In /users middleware');
    res.send('<h1>From "/users" handler </h1>');
});

app.use('/', (req, res, next) => {
    console.log("Default handler");
    res.send('<h1>From default handler</h1>');
});

app.listen(3000);

从浏览器(Chrome和Edge)发出请求时控制台输出

Console output when a request is made from browser (both chrome and edge)

http://localhost:3000
******************
In interceptor
Default handler
In interceptor
Default handler
******************

http://localhost:3000/users
******************
In interceptor
In /users middleware
In interceptor
Default handler
******************

但是当使用curl发出请求时，我看不到多次调用

But when a request is made using curl, I don't see multiple invocations

curl http://localhost:3000
******************
In interceptor
Default handler
******************

curl http://localhost:3000/users
******************
In interceptor
In /users middleware
******************

有人可以解释为什么从浏览器发出请求时多次调用中间件功能吗?

Can someone explain why middleware functions are invoked multiple times when request is made from browser?

推荐答案

从浏览器加载页面时看到多个请求的常见原因是两件事之一:

The usual reasons you see multiple requests when a page loads from a browser are one of two things:

1. 浏览器自动请求favicon.ico文件.
2. 浏览器尝试从HTML文件(脚本文件，图像，CSS文件等)中加载某些资源

通过添加以下内容，您可以确切地看到每个请求的目的:

You can see exactly what each request is for by adding:

console.log(req.url);

到您的中间件.

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