在Angular和Node.JS中实现实时输入验证的正确方法是什么？

<form #myForm="ngForm">
  <input type="text" name="username" [(ngModel)]="username" required minlength="5" maxlength="10">
  <div *ngIf="myForm.controls.username.invalid && (myForm.controls.username.dirty || myForm.controls.username.touched)">
    <div *ngIf="myForm.controls.username.errors.required">用户名不能为空</div>
    <div *ngIf="myForm.controls.username.errors.minlength">用户名长度不能少于5个字符</div>
    <div *ngIf="myForm.controls.username.errors.maxlength">用户名长度不能超过10个字符</div>
  </div>
</form>

const express = require('express');
const app = express();

app.use(express.json());

app.post('/validate', (req, res) => {
  const { username } = req.body;
  
  // 输入验证逻辑
  if (!username || username.length < 5 || username.length > 10) {
    return res.status(400).json({ error: '用户名验证失败' });
  }
  
  // 继续处理请求
  // ...
});

app.listen(3000, () => {
  console.log('Server started on port 3000');
});