Implement lbry.call() and get balance display working

js/gui.js

@@ -101,12 +101,23 @@ var logoStyle = {
 };
 
 var Header = React.createClass({
+  getInitialState: function() {
+    return {
+      balance: 0
+    };
+  },
+  componentDidMount: function() {
+    lbry.getBalance(function(balance) {
+      this.setState({
+        balance: balance
+      });
+    }.bind(this));
+  },
   render: function() {
-    var balance = lbry.getBalance();
     return (
       <header>
         <span style={balanceStyle}>
-          <CreditAmount amount={balance}/>
+          <CreditAmount amount={this.state.balance}/>
         </span>
         <div style={logoStyle}>
           <img src="../../web/img/lbry-dark-1600x528.png" style={imgStyle}/>

js/lbry.js

@@ -8,11 +8,24 @@ var lbry = {
 
 lbry.call = function (method, params, callback)
 {
-  /*
-   * XHR magic
-   */
-  //when XHR returns and is successful
-  // callback(JSON.parse(xhr.responseText));
+  var xhr = new XMLHttpRequest;
+  xhr.addEventListener('load', function() {
+    // The response from the HTTP endpoint has a "result" key containing a JSON string of the output of the JSON-RPC method itself
+    var method_output = JSON.parse(JSON.parse(xhr.responseText).result);
+
+    if (method_output.code !== 200) {
+        throw new Error('Call to method ' + method + ' failed with message: ' + method_output.message);
+    }
+
+    callback(method_output.result);
+  });
+  xhr.open('POST', 'http://localhost:5279/lbryapi', true);
+  xhr.send(JSON.stringify({
+    'jsonrpc': '2.0',
+    'method': method,
+    'params': params,
+    'id': 0
+  }));
 }
 
 //core