Uncaught SyntaxError: Unexpected token v in JSON at position 0
at JSON.parse (<anonymous>)
at XMLHttpRequest.xhr.onreadystatechange (cart.js:64)
xhr.onreadystatechange @ cart.js:64

xhr.onreadystatechange = function(){
  if(responded) return
  if(xhr.readyState == 4){
    responded = true
    if(xhr.status == 200) callback(null, JSON.parse(xhr.responseText))
    else callback(new Error(xhr.responseText))
  }
}

if(xhr.status == 200) callback(null, JSON.parse(xhr.responseText))

JSON.parse('v');