user3029: Is there a bitcoin library or even just pure javascript way of signing and verifying you own a btc address? 

user26873: bitcoinjs-lib and bitcore-lib are both javascript libraries that allow for key signing. 
For example with bitcore-lib:
var Message = require('bitcore-message');

var privateKey = new bitcore.PrivateKey('L23PpjkBQqpAF4vbMHNfTZAb3KFPBSawQ7KinFTzz7dxq6TZX8UA');
var message = new Message('This is an example of a signed message.');

var signature = message.sign(privateKey);

EDIT: To also include the verification example from bitcore's github. 
var Message = require('bitcore-message');

var address = '13Js7D3q4KvfSqgKN8LpNq57gcahrVc5JZ';
var signature = 'IBOvIfsAs/da1e36W8kw1cQOPqPVXCW5zJgNQ5kI8m57FycZXdeFmeyoIqJSREzE4W7vfDmdmPk0HokuJPvgPPE=';

var verified = new Message('This is an example of a signed message.').verify(address, signature);


3029: <p>Is there a bitcoin library or even just pure javascript way of <strong>signing</strong> and <strong>verifying</strong> you own a btc address? </p>
 26873: <p><a href="https://github.com/bitcoinjs/bitcoinjs-lib" rel="nofollow noreferrer">bitcoinjs-lib</a> and <a href="https://github.com/bitpay/bitcore-lib" rel="nofollow noreferrer">bitcore-lib</a> are both javascript libraries that allow for key signing. </p>

<p>For example with bitcore-lib:</p>

<pre><code>var Message = require('bitcore-message');

var privateKey = new bitcore.PrivateKey('L23PpjkBQqpAF4vbMHNfTZAb3KFPBSawQ7KinFTzz7dxq6TZX8UA');
var message = new Message('This is an example of a signed message.');

var signature = message.sign(privateKey);
</code></pre>

<p>EDIT: To also include the verification example from bitcore's github. </p>

<pre><code>var Message = require('bitcore-message');

var address = '13Js7D3q4KvfSqgKN8LpNq57gcahrVc5JZ';
var signature = 'IBOvIfsAs/da1e36W8kw1cQOPqPVXCW5zJgNQ5kI8m57FycZXdeFmeyoIqJSREzE4W7vfDmdmPk0HokuJPvgPPE=';

var verified = new Message('This is an example of a signed message.').verify(address, signature);
</code></pre>
