Converting ArrayBuffer to Base64-encoded String for Multipart Post

To efficiently convert an ArrayBuffer to a base64 string suitable for multipart posts, developers can leverage the following techniques:

Native Implementation

The first approach involves utilizing native functionality:

function _arrayBufferToBase64( buffer ) {
    var binary = '';
    var bytes = new Uint8Array( buffer );
    var len = bytes.byteLength;
    for (var i = 0; i 
Non-Native Implementation
If native implementation is not supported or requires speed optimization, consider using non-native methods:
// Refer to external library or gist for non-native implementation
Performance Comparison
Non-native implementations often exhibit higher performance as demonstrated in benchmarks:

• [JS Perf](https://jsperf.com/encoding-xhr-image-data/6)
• [JS Bench](https://jsben.ch/wnaZC)

However, developers should assess the performance and browser compatibility before choosing a particular approach.