valueKey

It is used only for combo.
The data value name by which to filter and get/edit data.

Example:

columns: [{
...
},{
  index: 'state',
  title: 'State',
  type: 'combo',
  width: 110,
  displayKey: 'text',
  valueKey: 'value',
  data: {
    proxy: {
      url: 'states.json'
    }
  }
...

states.json
{
  "data": [{
    "value": "",
    "text": ""
  },{
    "value": "AL",
    "text": "Alabama"
  },{
    "value": "AK",
    "text": "Alaska"
  },{
    "value": "AZ",
    "text": "Arizona"
  ...

Default

Only for column combo type.

undefined