How to turn a gallery image into BASE64

Question

I have a function that takes the image from the gallery and the camera and sends it to an area where the user can view it.

    import React, {useState} from 'react';
    import {View, TouchableOpacity, Text, StyleSheet, Image} from 'react-native';
    
    import ImagePicker from 'react-native-image-picker';
    
    export default function Upload() {
      const [avatar, setAvatar] = useState();
    
      function imagePickerCallback(data) {
        if (data.didCancel) {
          return;
        }
    
        if (data.error) {
          return;
        }
    
        if (!data.assets[0].uri) {
          return;
        }
    
        setAvatar(data.assets[0]);
      }
    
      return (
        <View style={styles.container}>
          <Image
            source={{
              uri: avatar
                ? avatar.uri
                : 'https://mltmpgeox6sf.i.optimole.com/w:761/h:720/q:auto/https://redbanksmilesnj.com/wp-content/uploads/2015/11/man-avatar-placeholder.png',
            }}
            style={styles.avatar}
          />
          <TouchableOpacity
            style={styles.button}
            onPress={() =>
              ImagePicker.launchCamera(imagePickerCallback)
            }>
            <Text style={styles.buttonText}>camera</Text>
          </TouchableOpacity>
    
          <TouchableOpacity
            style={styles.button}
            onPress={() =>
              ImagePicker.launchImageLibrary(imagePickerCallback)
            }>
            <Text style={styles.buttonText}>galery</Text>
          </TouchableOpacity>
    
        </View>
      );
    }

I am filling the source of the image with the URI obtained when picking up the image from the gallery or when taking a photo with the camera. My question is, how to turn this image into BASE64 to send it to firebase?

If necessary to install some library, please inform.