Hello I am trying to design a very simple web application with `Express.js` that just sends your email address that you submitted to the server side. But when I try to combine normal JavaScript (like `querySelector`) with code that has `Express.js` contents, it does not work and crashes saying that `document` in `document.getElementById("email")` is not defined. May I ask if there is a way to do this? Or how should I send data from the client side to the server side and vice versa properly?

This is my first very simple project in web development so the code is not the best.

**JavaScript Code**

```
const express = require("express")
const app = express();
const path = require("path")

app.use(express.static("./"))

app.listen(5000, () => {
    console.log("Server listening on port 5000...")
})

app.get("/", (req, res) => {
    res.sendFile("index.html", (err) => {
          console.log(err)
    })
})

let enterEmail = document.getElementById("email")

let submit = document.getElementById("submit")
let status = document.getElementById("status")

let email;

submit.addEventListener("click", (e) => {
    email = enterEmail.value 
    enterEmail.value = ""
    status.innerHTML = "Submitted email: " + email;
})

```

**HTML Code**

```
<!DOCTYPE html>
<html>
    <head>
    <link rel="stylesheet" href="./styles.css">
    </head>
    <body>

        <input id ="email" placeholder="enter email" type="text"></input>
        <input id="submit" type="submit">
        <h1 id="status">Submitted email: </h1>

        <script src="./index.js"></script>

    </body>
</html>

```

**The error message:**

```
let enterEmail = document.getElementById("email")
                 ^

ReferenceError: document is not defined
    at Object.<anonymous> (C:\Users\Lenovo\Desktop\personal-projects\app.js:23:18)
    at Module._compile (node:internal/modules/cjs/loader:1103:14)
    at Object.Module._extensions..js (node:internal/modules/cjs/loader:1155:10)
    at Module.load (node:internal/modules/cjs/loader:981:32)   
    at Function.Module._load (node:internal/modules/cjs/loader:822:12)
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:77:12)
    at node:internal/main/run_main_module:17:47
[nodemon] app crashed - waiting for file changes before starting...

```