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The Node.js template for OpenFaaS uses Express.js under the hood and the LTS version of Node, but provides an abstraction where you just work with an event and context object.

The event is used to obtain the original HTTP request, and the context is used to set the HTTP response. The underlying Express.js object is an implementation detail, and so is not available to the function author.

Async/await is supported by the handler by default.

The most thorough and complete examples for JavaScript/Node for OpenFaaS are in Alex Ellis' eBook: Serverless for Everyone Else

This is an official template maintained by OpenFaaS Ltd.

Create a new function

Create a new function using the template:

faas-cli template pull
faas-cli new --lang node18 echo

You'll find a new folder called echo with a handler.js and package.json file inside.

'use strict'

module.exports = async (event, context) => {
  const result = {
    'body': JSON.stringify(event.body),
    'content-type': event.headers["content-type"]

  return context

The Event object

The event object has the following properties:

  • event.body - the body of the HTTP request, either as a string or a JSON object
  • event.headers - the HTTP headers as a JSON object, index them as a dictionary i.e. event.headers["content-type"]
  • event.method - the HTTP method as a string
  • event.query - the query string as a JSON object, index them as a dictionary i.e. `event.query
  • event.path - the path of the HTTP request

The Context object

The context object has the following methods:

  • context.status(code) - set the HTTP status code
  • context.succeed(result) - set the HTTP response body, and end the request
  • - set the HTTP status code to 500, and end the request
  • context.headers(headers) - set the HTTP headers, pass in a JSON object

You may wish to combine the context.headers() method with the context.succeed() method to set the content-type header.

Or to combine the context.status() method with the context.succeed() method to set an alternative successful HTTP status code such as a 201.

Install packages

To install packages, cd into the function folder and run npm install --save:

faas-cli new --lang node18 http-req
cd http-req

npm install --save axios

Edit the handler.js:

'use strict'

const axios = require('axios')

module.exports = async (event, context) => {
  if(!event.body.url) {
    return context
      .fail('Missing .url in request body')

  var result = {}

  try {
    const res = await axios({"method": "GET", "url": event.body.url, validateStatus: () => true})
    result["body"] =
    result["status"] = res.status
  } catch (e){
    return context

  return context

Run the function with faas-cli local-run, and then test it out with a valid JSON input:

curl -i \
    -H "Content-type: application/json" \
    --data '{"url":""}'

As you can see from the example, when a valid JSON input is used in the request, along with an appropriate "Content-type" header, the event.body will transform into an object, which can be indexed as a dictionary.

Authenticate a function

By using the standard Authorization header, a function can be authenticated with a pre-shared secret.

Create a new pre-shared secret:

openssl rand -base64 32 > node-fn-token.txt

Then create a new secret in OpenFaaS:

faas-cli secret create node-fn-token --from-file node-fn-token.txt

Create a new function using the node18 template:


faas-cli new --lang node18 node-fn

Then edit the node-fn/handler.js:

'use strict'

const fs = require('fs').promises;
const tokenSecretName = "node-fn-token"

module.exports = async (event, context) => {

  let token = await fs.readFile(`/var/openfaas/secrets/${tokenSecretName}`, 'utf8')
  token = token.trim()

  if(!event.headers.authorization) {
    return context

  if(event.headers.authorization !== "Bearer " + token) {
    return context

  return context

Edit node-fn.yml and add the secrets section:

    lang: node18
    handler: ./node-fn
+    secrets:
+    - node-fn-token

Now test out the function with local-run or faas-cli up.

With local-run:

mkdir -p .secrets
cp node-fn-token.txt .secrets/node-fn-token

faas-cli local-run -f node-fn.yml

Try it out:

curl -i \
  -H "Authorization: Bearer $(cat node-fn-token.txt)"

HTTP/1.1 200 OK

When you test the function with faas-cli up, make sure you use the function's full URL.

Unit tests

Unit tests provide a quick and efficient way to exercise your code on your local computer, without needing to run faas-cli build or to deploy the function to a remote cluster.

With the node18 template, any unit tests that you provide will be run automatically upon each invocation of faas-cli build.

By default, an empty test step is written to package.json inside your function's handler folder, you can override this with your own command or test runner.

For example:

  "name": "function",
  "version": "1.0.0",
  "description": "",
  "main": "handler.js",
  "scripts": {
    "test": "mocha test/test.js"
  "keywords": [],
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "chai": "^4.2.0",
    "mocha": "^7.0.1"

Then create at least one test file such as: function-name/test/test.js:

var chai = require("chai")
var expect = chai.expect;

describe('MyFunction', function() {

If the tests fail, this will also fail the build of your function and prevent it from passing.

For a more detailed example, see: Serverless for Everyone Else

Access the raw body

Set the environment variable RAW_BODY to true to set the context.body to the original request body rather than the default behavior of parsing it as JSON.

This is useful where the original body needs to be passed to the function code without any parsing or processing. For instance, when working with binary data, or verifying the signature of a webhook.

    RAW_BODY: true

The raw body has a default maximum size of 100KB to prevent abuse from users. This can be configured manually to deal with larger payloads:

    RAW_BODY: true
    MAX_RAW_SIZE: 512kb

Set the maximum JSON request body size

Change the maximum size of a JSON request body by setting the environment variable MAX_JSON_SIZE. The default value is '100kb'

Note: the value must be enclosed in quotes ' '

This is useful when the function is expected to receive large amounts of JSON data in a single request. For instance, when working with large data sets and complex object types.

    MAX_JSON_SIZE: '5mb'