How to debug aws lambda functions written in node js

Question

We have been developing AWS Lambda functions in Node JS for a few months. Can we debug, i.e. step through the Node JS code as we can with .Net C# code in Visual Studio?

Answer 1

Debugging lambda using breakpoints in VSCode:

First, write test cases for your handler as follows: index.test.js

'use strict';

const handler = require('../index');

const chai = require('chai');

const { expect } = chai;

describe('debug demo', () => {
  it('should return success', () => {
    let event = {data: "some data"}
    handler(event, '', function(err, res) {
      expect(res.statusCode, '200')
    });
  });
});

Now add the VSCode debugger configuration

Step 1: Click on debugger icon on the left side

Step 2: Click Add configurations

and add the following configurations in launch.json file:

{
    "version": "0.2.0",
    "configurations": [

      {
          "type": "node",
          "request": "launch",
          "name": "Mocha All",
          "program": "${workspaceFolder}/node_modules/mocha/bin/_mocha",
          "args": [
              "--timeout",
              "999999",
              "--colors",
              "'${workspaceFolder}/lambda-codebase/**/test/*.test.js'"
          ],
          "console": "integratedTerminal",
          "internalConsoleOptions": "neverOpen"
      },
      {
          "type": "node",
          "request": "launch",
          "name": "Mocha Current File",
          "program": "${workspaceFolder}/node_modules/mocha/bin/_mocha",
          "args": [
              "--timeout",
              "999999",
              "--colors",
              "${file}"
          ],
          "console": "integratedTerminal",
          "internalConsoleOptions": "neverOpen"
      }
    ]
  }

Step 3: Now add a breakpoint to code which you wants to debug as follows:

Step 4: Now focus on the test file by clicking on the file:

Step 5: Choose the option from the drop-down "Mocha All" to run the complete solution and "Mocha current file" to run only selected file

Now click on the DEBUG Play button and enjoy the debugging!