js對象空值移除

function toType(obj) {
  return ({}).toString.call(obj).match(/\s([a-zA-Z]+)/)[1].toLowerCase()
}
function filterNull(o) {
  for (var key in o) {
    if (o[key] === null || o[key] === '' || o[key] === undefined) {
      delete o[key]
    }
    if (toType(o[key]) === 'string') {
      o[key] = o[key].trim()
    } else if (toType(o[key]) === 'object') {
      o[key] = filterNull(o[key])
    } else if (toType(o[key]) === 'array') {
      o[key] = filterNull(o[key])
    }
  }
  return o
}