Develop Reference

Lambda function with additional dependencies

I'm starting a CDK lambda project which gets the source code like this:
code: lambda.Code.fromAsset("resources"),
handler: "synthetic_test.main",
There's a single javascript file synthetic_test.js in that folder.
This seems to work but I can't figure out how to make it so that I could do:
const axios = require("axios");
in that file.
For some reason it seems to be able to import:
const AWS = require("aws-sdk");
but nothing else.
I did yarn add axios which added it to the package.json of my CDK project. But that does not really seem to help the lambda a lot.

The AWS Lambda runtime environment includes native language libraries and the relevant language-specific AWS SDK.
It does not contain arbitrary third-party packages. You need to either package those dependencies with your code or create a Lambda Layer that includes the dependencies and configure your Lambda function to use the Lambda Layer.
To package CDK app dependencies, see #aws-cdk/aws-lambda-nodejs and here.

I went with packaging dependencies with my code
My cdk went to
// 👇 define PUT account function
const putAccountLambda = new lambda.Function(this, "put-account-lambda", {
runtime: lambda.Runtime.NODEJS_14_X,
handler: "main.handler",
code: lambda.Code.fromAsset(path.join(__dirname, "/../src/put-account/dist")),
environment: {
REGION,
ADMINS_TABLE,
ADMINS_TABLE_PARTITION_KEY,
HASH_ALG,
}
})
With dist being the folder with a packed main.js file. And this file has a handler entrypoint. I had to update the package.json of these lambdas with packed dependencies.
{
"name": "put-account",
"version": "1.0.0",
"description": "",
"main": "index.js",
"scripts": {
"build": "webpack --mode=production --env env=prod",
"build:dev": "webpack --mode=development --env env=dev"
},
"author": "",
"license": "ISC",
"devDependencies": {
"webpack": "^5.66.0",
"webpack-cli": "^4.9.1",
"webpack-merge": "^5.8.0"
},
"dependencies": {
"aws-sdk": "^2.1058.0",
"crypto": "^1.0.1",
"uuid": "^8.3.2"
}
}
And I updated the package.json of my cdk project to these scripts.
"build": "tsc && npm run build:webpack",
"build:webpack": "for file in ./src/*; do (cd $file && npm i && npm run build) & done",
"build:beta": "tsc && npm run build:webpack:beta",
"build:webpack:beta": "for file in ./src/*; do (cd $file && npm i && npm run build:dev) & done",
Notice that my file structure is as follows:
./
bin
lib
src
package.json
With src holding the source code for my project's lambdas.
I am not sure if you are familiar with webpack, but I have divided my webpack configuration in common, dev, prod.
A dev webpack configuration is specially useful for debugging because otherwise you lose line numbers among other useful information when something goes wrong on runtime.

Node.JS export ES Object into NPM package?

I have an ES5 object/function that I'm trying to use inside an NPM package. That object is in a namespace such as
MY_NAMESPACE.myObject = function(){...}
where MY_NAMESPACE is just an object. For the web, I'd just link a JS file where the object/function is and then do
let whatever = new MY_NAMESPACE.myObject();
I have saved the source as my_function.js.
I created a npm package like so, in order to install it in my app
{
"name": "whatever",
"version": "1.0.0",
"description": "",
"main": "index.js",
"scripts": {
"test": "echo \"Error: no test specified\" && exit 1"
},
"author": "whatever",
"license": "Apache-2.0",
"exports" :{
"./my_function.js" : "./my_function.js"
}
}
When I install the package locally, I can see that my_function.js is in node_modules/whatever
How can I now reference/import my_function.js inside my app, then be able to call
let whatever = new MY_NAMESPACE.myObject();
Some of the awful Node.JS documentation mentions .mjs files to add ES modules but can't find examples/tutorials... I'm also trying to not add anything like module.exports to the my_function.js because that file is updated constantly and used in a web/front end environment as well.
So basically, I'm trying to attach a .js file inside a NPM package and would like to have its content available in my app. I'm hoping that, adding something to the index.js of the package would render the objects declared in the file, available across my app... I just don't know where to go from here.

One pattern to expose the function would be using module.exports like this:
# my_function.js
MY_NAMESPACE = {};
MY_NAMESPACE.myObject = function(){...};
module.exports = MY_NAMESPACE;
And then it can be consumed by another module in the same directory as:
# consumer JS file
let MY_NAMESPACE = require('./my_function');
let test = new MY_NAMESPACE.myObject();
If you really want to package up my_function.js in a separate node.js package (for example, if you need to share it between projects), there are a few additional steps to take. This documentation is a good starting point.

How to properly expose subpaths in package.json using the ”exports” key?

I’ve released a NPM package which is a plugin for a framework where only the main entry of my package.json is needed for usage in the framework and its environment. I also want to be able to use a subpath of the plugin in order for users to be able to use the plugin outside of this framework as well, which will require that the main entry point is never initialized as there are framework specific dependencies used there which I don't want to initialize when using this plugin outside of the framework.
My project structure looks like this:
.
├── index.js
├── submodule.js
└── package.json
Source code for the sake of this example looks like this:
// index.js
export default function () {
return "foo";
}
// submodule.js
export default function () {
return "bar";
}
// package.json
{
"name": "my-package",
"version": "1.0.0",
"description": "",
"main": "index.js",
"type": "module",
"exports": {
".": "./index.js",
"./submodule": "./submodule.js"
},
"scripts": {
"test": "echo \"Error: no test specified\" && exit 1"
},
"keywords": [],
"author": "",
"license": "MIT"
}
According to Node.js documentation on this matter, this setup should allow me to use my package like this:
import myPackage from ’my-package’
import mySubModule from ’my-package/submodule’
In order to be able to test my package locally I run npm link in the project root of my npm package and then in another project i run npm link my-package. Now that I try to run the project (using parcel-bundler) that imports my-package and my-package/submodule like in the example above I get the following exception:
Cannot resolve dependency 'my-package/submodule'
I'm using NVM with Node v.12.18.4 and NPM v.7.15.0. I have also tried with Node v.14.17.0 but the issue persists. What am I missing?

It seems that the project setup is correct and that the problem lies in the parcel-bundler which does not support package.json#exports yet. There's currently an open issue on this matter.

package.json - how to determine what parts of the module are installed

I have a project structure like this:
__tests__
example
src
.bablerc
.eslintignore
.eslintrd
.gitignore
package.json
package-lock.json
README.md
and package.json parameters like:
{
"name": "",
"version": "0.0.1",
"description": "",
"main": "src/index.js",
"scripts": {
"test": "jest"
},
"files": [
"src/"
],
"repository": {
"type": "git",
"url": "url"
},
"jest": {
},
"devDependencies": {
},
"peerDependencies": {
}
}
When I npm install this modules I only get src folder with an empty index.js file. The goal was to only have the user install all of the src folder and not the example part since that is an example app. I thought that "files": ["src/"], would solve this. However it's not doing what I would expect. I don't see anything that is in the src folder. It's empty!
npm docs say:
The optional files field is an array of file patterns that describes
the entries to be included when your package is installed as a
dependency. File patterns follow a similar syntax to .gitignore, but
reversed: including a file, directory, or glob pattern (*, **/, and
such) will make it so that file is included in the tarball when it’s
packed. Omitting the field will make it default to [""], which means
it will include all file
How do I allow the user to install all of the src folder and ignore the example folder?
I'm on npm 5.6.0 and node v9.11.2

Almost there! Files entry behave like in a line a .gitignore. That works:
"files": ["src"]
For testing purposes, you can run npm pack --dry-run to check in the pack reports what files would be included when running npm install on the package you're developing.

Unable to require a React component

I am currently in the process of extracting modules from a monolithic React project so that they can be stored separately in my npm registry, but I can't seem to export and import them properly. Before trying to extract them, I was using:
const Component = require("./component.js");
and using webpack to bundle everything. That was working fine. I then moved the component to a separate project, which I bundled with webpack. I can't seem to get it to work as an npm dependency however. Here's the basic code for the component:
// Some require statements
...
var Component = React.createClass({...});
module.exports = Component;
The build process outputs the bundle to build/bundle.js, and the package.json looks like this:
{
"name": "component",
"version": "0.0.2",
"description": "...",
"main": "build/bundle.js",
"scripts": {
"test": "echo \"Error: no test specified\" && exit 1",
"build-dev": "webpack",
"build-min": "NODE_ENV=production webpack && uglifyjs ./build/bundle.js -c -m -o ./build/bundle.min.js --source-map ./build/bundle.min.js.map",
"prepublish": "npm run build-min"
},
"publishConfig": {
"registry": "registry"
},
"author": "esaron",
"license": "UNLICENSED",
"dependencies": {
...
},
"devDependencies": {
...
}
}
And I'm importing it with:
const Component = require("component");
When I try to load the page, I see the following error in the console:
bundle.js:1299 Uncaught Invariant Violation: Element type is invalid: expected a string (for built-in components) or a class/function (for composite components) but got: object. Check the render method of exports.
And when debugging, sure enough, the call to require is giving me
Component = Object {}
I get the same results if I require the bundle.js directly after copying it into the project, so I feel like I must just not be setting up my build and publish the right way, and after searching for a while, I wasn't able to find out what I was doing wrong.

You should not be bundling your components when they are separated out into their own packages. If they are using ES6, it's a good idea to transpile them using Babel as a prepublish step, but you do not need to bundle them.
Think about what the bundle step is doing to your component. It is going through your entry point and pulling in any required dependencies into a single file. That means that your bundle.js result will have pulled in all of react, react-dom, and anything else you required from your component.
Only your main application (which will be requiring the component packages) needs a bundle step. Here, it will resolve all dependencies including those that are nested and pull them together into your app's bundle.js, ensuring that you do not end up with duplicate copies of libraries like react pulled into your app.