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code-component

A code component forked from the elastic.io code-component, runs a piece of a JavaScript code inside your flow.

Available Variables and Libraries

Here are the available variables and libraries that can be used within the context of execution. The most up-to-date list can always be found in be used within the context of execution or in code.js of the component. Below is a sample for the reference. Built-in Node.js global objects are also supported.

Elastic.io Specific Functionality

  • msg - incoming message containing the payload from the previous step
  • cfg - step's configuration. At the moment contains only one property: code (the code, being executed). May contain further attributes passed through the fields propery in the flow definition
  • snapshot - step's snapshot
  • messages - utility for convenient message creation
  • emitter user to emit messages and errors

Other Libraries/functions

  • wait(numberOfMilliscondsToSleep) - Utility function for sleeping
  • request - Http Client (wrapped in co - this library so that it is pre-promisified)
  • _ - Lodash

Code component usage Examples

Use code is very simple, just do following:

async function run(msg, cfg, snapshot) {
  this.logger.info('Incoming message is %j', msg);
  const data = { result : 'Hello world!' };
  // You can emit as many data messages as required
  await this.emit('data', { data });
  this.logger.info('Execution finished');
}

Please note if you have a simple one-in-one-out function you can simply return a JSON object as a result of your function, it will be automatically emitted as data.

Common usage scenarios

Doing complex data transformation

JSONata is great however sometimes it's easier to do things in JavaScript, if you want to transform an incoming message with code, just use following sample:

async function run(msg, cfg, snapshot) {
  return {
      addition: 'You can use code',
      keys: Object.keys(msg)    
  };
}

Calling an external REST API

It's very simple to code a small REST API call out of the Code component, see following example:

async function run(msg, cfg, snapshot) {
  const res = await request.get({
    uri: 'https://postman-echo.com/get?foo1=bar1&foo2=bar2',
    json: true  
  });
  return {
    arguments: res.body.args
  }
}