完整代码

//1.引入http的模块
var http= require('http');
var fs=require('fs');//读取页面内容
var path=require('path');//拼接
const { throws } = require('assert');
//2.创建服务器
var server= http.createServer();
//3.启动服务器
server.listen(3000,function () {
    console.log('server  ....   start.. success');
});

//4.监听客户发送过来的请求，并相应数据给客户端   request(请求对象)  response(响应对象)
server.on('request',function (request,response) {
    //获取的请求路径
    var url= request.url;
    //响应乱码处理
    //response.setHeader("cont")
    if(url==='/login'){
        //读取文件  nodeDeme/static/login.html
        fs.readFile(path.join(__dirname,'static/login.html'),'utf8',function (err,data) {
            if(err){
                throw err;
            }
            response.end(data);
        });

    }else if(url==='/register'){
        fs.readFile(path.join(__dirname,'static/register.html'),'utf8',function (err,data) {
            if(err){
                throw err;
            }
            response.end(data);
        });
    }
    else if(url==='/'){
        fs.readFile(path.join(__dirname,'static/index.html'),'utf8',function (err,data) {
            if(err){
                throw err;
            }
            response.end(data);
        });
    }
    else if(url==='/add'){
        fs.readFile(path.join(__dirname,'static/add.html'),'utf8',function (err,data) {
            if(err){
                throw err;
            }
            response.end(data);
        });
    }else {
        fs.readFile(path.join(__dirname,'static/404.html'),'utf8',function (err,data) {
            if(err){
                throw err;
            }
            response.end(data);
        });
    }

});

改进之后

//1.引入http模块 path模块（拼接路径） fs模块 文件读写
var http = require('http');
var fs = require('fs');
var path = require('path');
const { ifError } = require('assert');
//2.创建服务器
var serve = http.createServer();
//3.启动服务器
serve.listen(3000,function(){
    console.log('server start success!')
});
//4.监听客户端发来的请求
serve.on('request',function(request,response){
    //获取请求路径
    var url = request.url;
    //根据不同的请求，找对应的页面
       var filepath;
    if(url==='/'){
        filepath =  path.join(__dirname,'public/index.html');
        //读取页面内容
        fs.readFile(filepath,'utf8',function(err,data){
            if(err){
                throw err;
            }else{
                response.end(data);
            }
        })
    }else{
        if(url.indexOf('.')>=0){
            filepath= path.join(__dirname,'public',url);
        }else{
            filepath= path.join(__dirname,'public',url+'.html');
        }
        //读取页面内容
        fs.readFile(filepath,'utf8',function(err,data){
            if(err){
                throw err;
            }else{
                response.end(data);
            }
        })
    }
})