Enumerate SPWeb properties in JSOM

EnumWebProps.js

var context = SP.ClientContext.get_current()
var web = context.get_web()
var props = web.get_allProperties()
context.load(web)
context.load(props)
context.executeQueryAsync(
  function () {
      var t = "Properties\n"
      
      for (var z in props.get_fieldValues()) {
          t += z + ": " + props.get_item(z) + "\n"
      }
      alert(t)
  },
  function () {
      alert('Error')
  })