Firebase: Firebase App named '[DEFAULT]' in JS

Im trying to connect my project with Cloud Firestore, but when i put the necesary code, bring me this error:

errors.ts:91 Uncaught FirebaseError: Firebase: Firebase App named '[DEFAULT]' already exists (app/duplicate-app).
at initializeApp (https://www.gstatic.com/firebasejs/8.6.2/firebase-app.js:1:17950)
at Object.H.initializeApp (https://www.gstatic.com/firebasejs/8.6.2/firebase-app.js:1:21516)
at file:///C:/Users/Angel/Desktop/Imagine/index.js:28:10

The code that i put was:

firebase.initializeApp({
  apiKey: "myapikey",
  authDomain: "mydomain",
  projectId: "myprojectid"
});

var db = firebase.firestore();

db.collection("users").add({
  first: "Ada",
  last: "Lovelace",
  born: 1815
})
.then((docRef) => {
  console.log("Document written with ID: ", docRef.id);
})
.catch((error) => {
  console.error("Error adding document: ", error);
});