How to test for equality in ArrayBuffer, DataView, and TypedArray

Question

Is there a way how to test if two JavaScript ArrayBuffers are equal? I would like to write test for message composing method. The only way I found is to convert the ArrayBuffer to string and then compare. Did I miss something?

Following code is giving false, even if I think that it should be true:

(function() {
    'use strict';

    /* Fill buffer with data of Verse header and user_auth
     * command */
    var buf_pos = 0;
    var name_len = 6
    var message_len = 4 + 1 + 1 + 1 + name_len + 1;

    var buf = new ArrayBuffer(message_len);
    var view = new DataView(buf);
    /* Verse header starts with version */
    view.setUint8(buf_pos, 1 << 4); /* First 4 bits are reserved for version of protocol */
    buf_pos += 2;
    /* The lenght of the message */
    view.setUint16(buf_pos, message_len);
    buf_pos += 2;

    buf_pos = 0;
    var buf2 = new ArrayBuffer(message_len);
    var view2 = new DataView(buf);
    /* Verse header starts with version */
    view2.setUint8(buf_pos, 1 << 4); /* First 4 bits are reserved for version of protocol */
    buf_pos += 2;
    /* The lenght of the message */
    view2.setUint16(buf_pos, message_len);
    buf_pos += 2;


    if(buf == buf2){
        console.log('true');
    }
    else{
        console.log('false');
    }


}());

If I try to compare view and view2 it's false again.

Answer 1

You cannot compare two objects directly in JavaScript using == or ===.
These operators will only check the equality of references (i.e. if expressions reference the same object).

You can, however, use DataView or ArrayView objects to retrieve values of specific parts of ArrayBuffer objects and check them.

If you want to check headers:

if (  view1.getUint8 (0) == view2.getUint8 (0)
   && view1.getUint16(2) == view2.getUint16(2)) ...

Or if you want to check the globality of your buffers:

function equal (buf1, buf2)
{
    if (buf1.byteLength != buf2.byteLength) return false;
    var dv1 = new Int8Array(buf1);
    var dv2 = new Int8Array(buf2);
    for (var i = 0 ; i != buf1.byteLength ; i++)
    {
        if (dv1[i] != dv2[i]) return false;
    }
    return true;
}

If you want to implement a complex data structure based on ArrayBuffer, I suggest creating your own class, or else you will have to resort to cumbersome raw DataView / ArrayView instances each time you will want to move a matchstick in and out of the structure.