Creates a DataBuffer object that is binary-compatible with Java's DataOutputStream, also sports a function that automatically creates a Lavaplayer-compatible base64 string. Example usage at the bottom.

DataBuffer.js

class DataBuffer {
    constructor() {
        this.bytearr = [];
    }

    write(byte) {
        this.bytearr.push(byte)
    }

    writeByteArray(byteArray) {
        for(let i = 0; i < byteArray.length; i++) {
            this.write(byteArray[i]);
        }
    }

    writeInt(int) {
        this.write((int >>> 24) & 0xFF);
        this.write((int >>> 16) & 0xFF);
        this.write((int >>>  8) & 0xFF);
        this.write((int >>>  0) & 0xFF);
    }

    getWriteInt(int) {
        return [
            (int >>> 24) & 0xFF,
            (int >>> 16) & 0xFF,
            (int >>> 8) & 0xFF,
            (int >>> 0) & 0xFF
        ]
    }

    writeLong(long) {
        this.write(rshift(long, 56) & 0xFF);
        this.write(rshift(long, 48) & 0xFF);
        this.write(rshift(long, 40) & 0xFF);
        this.write(rshift(long, 32) & 0xFF);
        this.write(rshift(long, 24) & 0xFF);
        this.write(rshift(long, 16) & 0xFF);
        this.write(rshift(long,  8) & 0xFF);
        this.write(rshift(long,  0) & 0xFF);
    }

    writeBoolean(bool) {
        this.write(bool ? 1 : 0);
    }

    // https://gist.github.com/joni/3760795/8f0c1a608b7f0c8b3978db68105c5b1d741d0446
    writeUTF8(str) {
        let utf8 = [];
        utf8.push((str.length >>> 8) & 0xFF)
        utf8.push((str.length >>> 0) & 0xFF)
        for (let i = 0; i < str.length; i++) {
            let charcode = str.charCodeAt(i);
            if (charcode < 0x80) utf8.push(charcode);
            else if (charcode < 0x800) {
                utf8.push(0xC0 | (charcode >> 6), 0x80 | (charcode & 0x3f));
            }
            else if (charcode < 0xd800 || charcode >= 0xe000) {
                utf8.push(0xE0 | (charcode >> 12),
                    0x80 | ((charcode>>6) & 0x3f),
                    0x80 | (charcode & 0x3f));
            }
            // surrogate pair
            else {
                i++;
                charcode = ((charcode&0x3ff)<<10)|(str.charCodeAt(i)&0x3ff)
                utf8.push(0xf0 | (charcode >>18),
                    0x80 | ((charcode>>12) & 0x3f),
                    0x80 | ((charcode>>6) & 0x3f),
                    0x80 | (charcode & 0x3f));
            }
        }
        this.writeByteArray(utf8)
    }

    getLavaplayerBase64() {
        let binary = '';

        // Need to add a prefix in front of the entire byte array that determines the length, use flag '1'
        let lengthBytes= this.getWriteInt(this.bytearr.length | (1 << 30));  // the prefix
        let byteArr = this.bytearr  // other bytes

        // put that prefix in front of the other bytes
        let totalBytes = [...lengthBytes, ...byteArr]

        // convert to a ByteBuffer
        let totalBytesArrayBuffer = new Uint8Array(totalBytes);

        let len = totalBytesArrayBuffer.byteLength;
        for (let i = 0; i < len; i++) {
            binary += String.fromCharCode( totalBytesArrayBuffer[ i ] );
        }
        //convert to base64
        return window.btoa( binary );
    }
}

/*
We can't use the >>> and <<< operators here because JavaScript only allows bitwise shift for 32bit values
 */

function rshift(number, shift) {
    return Math.floor(number / Math.pow(2, shift));
}

export default DataBuffer;

/*
EXAMPLE USAGE

    let dataBuffer = new DataBuffer();
    dataBuffer.write(2);
    dataBuffer.writeUTF8(track.title);
    dataBuffer.writeUTF8(track.artist);
    dataBuffer.writeLong(track.duration);
    dataBuffer.writeUTF8(track.videoID);
    dataBuffer.writeBoolean(false);
    dataBuffer.writeBoolean(true);
    dataBuffer.writeUTF8(track.url);
    dataBuffer.writeUTF8("youtube");
    dataBuffer.writeLong(0);

    return dataBuffer.getLavaplayerBase64() 
 
*/