Determine is the slug field value changed
function hasChanged(newData, oldData) {
    var changed = false
    for (var i = 0; i < scope.length; i++) {
      var k = scope[i],
        newVal = _.get(newData, k),
        oldVal = _.get(oldData, k)
      if (!_.isEqual(newVal, oldVal)) {
        changed = true
        break
      }
    }

    return changed
  }