Convert array buffer to base64 string

arrayBufferToBase64.js

function arrayBufferToBase64(buffer) {
    let binary = '';
    let bytes = new Uint8Array(buffer);
    let len = bytes.byteLength;
    for (let i = 0; i < len; i++) {
        binary += String.fromCharCode(bytes[i]);
    }
    return window.btoa(binary);
}

     let base64String = btoa(String.fromCharCode(...file));

btoa() is deprecated

btoa() is deprecated

Can you give your source please ?
https://developer.mozilla.org/en-US/docs/Web/API/btoa