Custom

Function definitions](#function-definition) type property defines a list of function types that are set by the specification.

Some runtime implementations might support additional function types that extend the ones defined in the specification. In those cases you can define a custom function type with for example:

{
"functions": [
  {
    "name": "send-order-confirmation",
    "operation": "/path/to/my/script/order.ts#myFunction",
    "type": "custom"
  }
]
}

In this example we define a custom function type that is meant to execute an external TypeScript script.

When a custom function type is specified, the operation property value has a custom format, meaning that its format is controlled by the runtime which provides the custom function type.

Later, the function should be able to be used in an action as any other function supported by the specification:

[{
  "states": [{
      "name": "handle-order",
      "type": "operation",
      "actions": [
        {
          "name": "send-order-confirmation",
          "functionRef": {
            "refName": "send-order-confirmation",
            "arguments": {
              "order": "${ .order }"
            }
          }
        }
      ],
      "transition": "emailCustomer"
  }]
}]

Note that custom function types are not portable across runtimes.