Text field validator only alpha

app.js

var win1 = Titanium.UI.createWindow({  
    title:'Tab 1',
    backgroundColor:'#fff'
});
win1.open();
 
var alphaonly = Titanium.UI.createTextField({
    color:'#336699',
    height:35,
    width:300,
    top:10,
    borderStyle:Titanium.UI.INPUT_BORDERSTYLE_ROUNDED,
    keyboardToolbarColor: '#999',   
    keyboardToolbarHeight: 40,
});
 
 
win1.add(alphaonly);
 
 
alphaonly.addEventListener('change', function(e){

  var invalidChars = /[0-9]/gi
  if(invalidChars.test(e.source.value)) {
      e.source.value = e.source.value.replace(invalidChars,"");
  }
});