Function isReserved

static/vuejs/vue.runtime.js:363–366

* Check if a string starts with $ or _

(str)

 * Check if a string starts with $ or _
 */
function isReserved (str) {
  var c = (str + '').charCodeAt(0);
  return c === 0x24 || c === 0x5F
}

/**
 * Define a property.