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Handler Function

The handler function is used to handle a fetched task.

const { Client, logger, Variables } = require("camunda-external-task-client-js");

// create a Client instance with custom configuration
const client = new Client({ baseUrl: "http://localhost:8080/engine-rest", use: logger });

// create a handler function
const handler = async function({ task, taskService }) {
  // get the process variable 'score'
  const score = Variables.get("score");
  // set a process variable 'winning'
  const processVariables = new Variables().set("winning", score > 5);
  // set a local variable 'winningDate'
  const localVariables = new Variables().set("winningDate", new Date());

  // complete the task
  await taskService.complete(task, processVariables, localVariables);
};

// susbscribe to the topic: 'topicName'
client.subscribe("topicName", handler);

task.variables

The variables object is a read-only Variables instance.
It provides various getters for reading the process variables in the scope of the service task.

client.subscribe("bar", async function({ task, taskService }) {
  // output all process variables
  console.log(task.variables.getAll());
});

taskService.complete(task, processVariables, localVariables)

Parameter Description Type Required
task task or id of the task to complete object or string ✓
processVariables map of variables to set in the process scope object
localVariables map of variables to set in the task scope object 
// Susbscribe to the topic: 'topicName'
client.subscribe("topicName", async function({ task, taskService }) {
  // Put your business logic

  // Complete the task
  await taskService.complete(task);
});

taskService.handleFailure(task, options)

Parameter Description Type Required
task task or id of the task to handle failure. object or string ✓
options options about the failure. object

options include:

Option Description Type Required Default
errorMessage An message indicating the reason of the failure. string
errorDetails A detailed error description. string
retries A number of how often the task should be retried. Must be >= 0. If this is 0, an incident is created and the task cannot be fetched anymore unless the retries are increased again. The incident's message is set to the errorMessage parameter. number
retryTimeout A timeout in milliseconds before the external task becomes available again for fetching. Must be >= 0. number 
// Susbscribe to the topic: 'topicName'
client.subscribe("topicName", async function({ task, taskService }) {
  // Put your business logic

  // Handle a Failure
  await taskService.handleFailure(task, {
    errorMessage: "some failure message",
    errorDetails: "some details",
    retries: 1,
    retryTimeout: 1000
  });
});

taskService.handleBpmnError(task, errorCode)

Parameter Description Type Required
task task or id of the task to handle bpmn failure object or string ✓
errorCode An error code that indicates the predefined error. Is used to identify the BPMN error handler. string ✓
errorMessage An error message that describes the error. string
variables Map of variables which will be passed to the execution. 
// Susbscribe to the topic: 'topicName'
client.subscribe("topicName", async function({ task, taskService }) {
  // Put your business logic

  // Create some variables
  const variables = new Variables().set('date', new Date());

  // Handle a BPMN Failure
  await taskService.handleBpmnError(task, "BPMNError_Code", "Error message", variables);
});

taskService.extendLock(task, newDuration)

Parameter Description Type Required
task task or id of the task to extend lock duration object or string ✓
newDuration An amount of time (in milliseconds). This is the new lock duration starting from the current moment. number ✓ 
// Susbscribe to the topic: 'topicName'
client.subscribe("topicName", async function({ task, taskService }) {
  // Put your business logic

  // Extend the lock time
  try {
    await taskService.extendLock(task, 5000);
    console.log("I extended the lock time successfully!!");
  } catch (e) {
    console.error(`Failed to extend the lock time, ${e}`);
  }
});

taskService.unlock(task)

Parameter Description Type Required
task task or id of the task to unlock object or string ✓ 
// Susbscribe to the topic: 'topicName'
client.subscribe("topicName", async function({ task, taskService }) {
  // Put your business logic

  // Unlock the task
  await taskService.unlock(task);
});

taskService.lock(task, newDuration)

Parameter Description Type Required
task task or id of the task to extend lock duration object or string ✓
duration An amount of time (in milliseconds). This is the lock duration starting from the current moment. number ✓ 
// Susbscribe to the topic: 'topicName'
client.subscribe("topicName", async function({ task, taskService }) {
  // Task is locked by default
  // Put your business logic, unlock the task or let the lock expire

  // Lock a task again
  try {
    await taskService.lock(task, 5000);
    console.log("I locked the task successfully!");
  } catch (e) {
    console.error(`Failed to lock the task, ${e}`);
  }
});