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add typescript webpack sample (#237)
* add the code and configurations * add the documentation
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‎lambda-hot-reloading/lambda-typescript-webpack/.eslintrc.js‎

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module.exports = {
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env: {
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browser: true,
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es6: true,
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node: true,
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},
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extends: [
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"standard",
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"eslint:recommended",
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"plugin:@typescript-eslint/recommended",
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"plugin:functional/recommended",
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"prettier",
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"plugin:prettier/recommended",
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],
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parser: "@typescript-eslint/parser",
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parserOptions: {
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project: "tsconfig.json",
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sourceType: "module",
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ecmaFeatures: {
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jsx: true,
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},
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},
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plugins: [
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"@typescript-eslint",
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"functional",
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"prettier",
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],
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rules: {
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"functional/no-conditional-statement": 0,
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},
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};

‎lambda-hot-reloading/lambda-typescript-webpack/.gitignore‎

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node_modules
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dist/
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lambda_function.zip

‎lambda-hot-reloading/lambda-typescript-webpack/.prettierignore‎

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# package.json is formatted by package managers, so we ignore it here
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package.json
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src/generated/

‎lambda-hot-reloading/lambda-typescript-webpack/.prettierrc.json‎

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{
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"printWidth": 120,
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"trailingComma": "es5",
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"tabWidth": 2,
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"semi": true,
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"singleQuote": false
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}

‎lambda-hot-reloading/lambda-typescript-webpack/README.md‎

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# Hot Reloading your Typescript Lambda with LocalStack & Webpack
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This is a simple example of how to hot reload your Typescript Lambda with Webpack with the help of LocalStack's Hot Reloading feature.
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## Pre-requisites
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* [LocalStack](https://docs.localstack.cloud/getting-started/installation)
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* [Docker](https://docs.docker.com/get-docker/)
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* [Node.js](https://nodejs.org/en/download/)
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* [AWS CLI](https://docs.aws.amazon.com/cli/latest/userguide/cli-chap-install.html)
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* [`awslocal`](https://github.com/localstack/awscli-local)
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* [yarn](https://classic.yarnpkg.com/en/docs/install)
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* `jq`
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## Start LocalStack
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Start your LocalStack Docker container with the following command:
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```bash
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localstack start
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```
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## Install dependencies
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Install the dependencies with the following command:
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```bash
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yarn install
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```
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## Build the Lambda
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Build the Lambda with the following command:
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```bash
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npm run build
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```
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Note that the `build` script is using Nodemon to watch for changes in the `src` directory and rebuild the Lambda. This would be useful when you are developing & testing your Lambda, while making changes to the code in real-time.
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With every change, you will see the following output:
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```bash
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yarn run build
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yarn run v1.22.19
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$ yarn run clean && yarn run webpack --watch
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$ rimraf dist/*
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$ cross-env TS_NODE_PROJECT="tsconfig.webpack.json" webpack --mode production --watch
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asset api.js 1.4 KiB [emitted] [minimized] (name: api)
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./src/api.ts 1.42 KiB [built] [code generated]
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./src/util.ts 314 bytes [built] [code generated]
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webpack 5.75.0 compiled successfully in 602 ms
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[nodemon] 3.0.1
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[nodemon] to restart at any time, enter `rs`
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[nodemon] watching path(s): dist/api.js
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[nodemon] watching extensions: js,mjs,cjs,json
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[nodemon] starting `node dist/api.js`
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[nodemon] clean exit - waiting for changes before restart
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asset api.js 1.4 KiB [emitted] [minimized] (name: api)
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./src/api.ts 1.42 KiB [built] [code generated]
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./src/util.ts 314 bytes [built] [code generated]
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webpack 5.75.0 compiled successfully in 455 ms
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[nodemon] restarting due to changes...
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[nodemon] starting `node dist/api.js`
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```
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## Deploy the Lambda
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Deploy the Lambda with the following command:
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```bash
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awslocal lambda create-function \
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--function-name localstack-example \
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--runtime nodejs18.x \
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--role arn:aws:iam::000000000000:role/lambda-ex \
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--code S3Bucket="hot-reload",S3Key="$(PWD)/dist" \
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--handler api.default
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```
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Additionally, you can create a Lambda Function URL with the following command:
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```bash
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function_url=$(awslocal lambda create-function-url-config --function-name localstack-example --auth-type NONE | jq -r '.FunctionUrl')
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```
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## Test the Lambda
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You can test the Lambda by sending `POST` requests to the Lambda Function URL:
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```bash
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curl -X POST \
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-H "Content-Type: application/json" \
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-d '{"name": "John", "age": 30}' \
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"$function_url"
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```
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The following output would be displayed:
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```bash
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{"payload":{"name":"John","age":30}}
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```
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You can additionally test the Lambda with the following command:
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```bash
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curl -X GET "$function_url"
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```
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This will return the following output:
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```bash
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{"error":"Only JSON payload is accepted"}
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```
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## Hot Reload the Lambda
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Go to the `src` directory and make changes to the `api.ts` file. For example, change the following line:
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```typescript
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return errorResponse("Only JSON payloads are accepted", 406);
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```
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Make the `errorResponse` function return `"Only JSON payload is accepted"` instead of `"Only JSON payloads are accepted"`. Save the file and run the last `curl` command again:
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```bash
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curl -X GET "$function_url"
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```
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This will return the following output:
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```bash
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{"error":"Only JSON payload is accepted"}
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```
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You can perform further changes to the `api.ts` file and test the Lambda in real-time.
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## How does it work?
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The Lambda Hot Reloading feature in LocalStack allows you to hot reload your Lambda code in real-time. In this sample, this is achieved using the following:
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- The `build` script in the `package.json` file uses Nodemon to watch for changes in the `src` directory and rebuild the Lambda. This is enabled using the [`nodemon-webpack-plugin`](https://www.npmjs.com/package/nodemon-webpack-plugin) plugin, which has been pre-configured in the `webpack.config.js` file.
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- The `S3Bucket` and `S3Key` parameters in the `awslocal lambda create-function` command are used to deploy the Lambda code from the `dist` directory. This is done by specifying the `dist` directory as the `S3Key` parameter. Everytime the Lambda is updated, Nodemon triggers another build and the `dist` directory is updated with the latest code changes. LocalStack then automatically updates the Lambda code with the latest changes from the `dist` directory.
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## Notes
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This sample application is inherited from a [public repository](https://github.com/pdlug/lambda-typescript-webpack).

‎lambda-hot-reloading/lambda-typescript-webpack/package.json‎

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{
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"name": "lambda-typescript-webpack",
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"version": "1.0.0",
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"main": "index.js",
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"license": "MIT",
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"scripts": {
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"build": "yarn run clean && yarn run webpack --watch",
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"build-aws": "yarn run clean && yarn run webpack",
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"clean": "rimraf dist/*",
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"lint": "eslint \"src/**/*.ts*\"",
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"lint:fix": "eslint --fix \"src/**/*.ts*\"",
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"format": "prettier *.ts \"src/**/*.ts*\" --write",
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"webpack": "cross-env TS_NODE_PROJECT=\"tsconfig.webpack.json\" webpack --mode production",
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"package": "zip -q -j -r ./lambda_function.zip dist"
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},
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"devDependencies": {
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"@types/aws-lambda": "^8",
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"@types/node": "^18",
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"@types/webpack": "^5",
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"@typescript-eslint/eslint-plugin": "^5",
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"@typescript-eslint/parser": "^5",
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"builtin-modules": "^3",
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"cross-env": "^7",
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"eslint": "^8",
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"eslint-config-prettier": "^8",
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"eslint-config-standard": "^17",
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"eslint-plugin-functional": "^4",
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"eslint-plugin-import": "^2",
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"eslint-plugin-n": "^15",
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"eslint-plugin-node": "^11",
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"eslint-plugin-prettier": "^4",
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"eslint-plugin-promise": "^6",
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"json-loader": "^0",
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"prettier": "^2",
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"rimraf": "^3",
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"ts-loader": "^9",
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"ts-node": "^10",
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"typescript": "^4",
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"webpack": "^5",
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"webpack-cli": "^5",
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"nodemon-webpack-plugin": "^4.8.2"
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},
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"dependencies": {
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"aws-sdk": "^2",
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"bufferutil": "^4",
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"utf-8-validate": "^6"
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}
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}

‎lambda-hot-reloading/lambda-typescript-webpack/run.sh‎

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#!/bin/bash
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awslocal lambda create-function \
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--function-name localstack-example \
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--runtime nodejs18.x \
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--role arn:aws:iam::000000000000:role/lambda-ex \
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--code S3Bucket="hot-reload",S3Key="$(PWD)/dist" \
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--handler api.default
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function_url=$(awslocal lambda create-function-url-config --function-name localstack-example --auth-type NONE | jq -r '.FunctionUrl')
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curl -X POST \
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-H "Content-Type: application/json" \
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-d '{"name": "John", "age": 30}' \
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"$function_url"
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curl -X GET "$function_url"

‎lambda-hot-reloading/lambda-typescript-webpack/src/api.ts‎

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import AWSLambda from "aws-lambda";
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import { downcaseKeys } from "./util";
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const errorResponse = (message: string, code = 500): AWSLambda.APIGatewayProxyResult => ({
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body: JSON.stringify({ error: message }),
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statusCode: code,
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});
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export default async (event: AWSLambda.APIGatewayEvent): Promise<AWSLambda.APIGatewayProxyResult> => {
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const headers = downcaseKeys(event.headers);
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if (!/^application\/json\b/.test(headers["content-type"] || "") || !event.body) {
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return errorResponse("Only JSON payloads are accepted", 406);
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}
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const payload = JSON.parse(event.body);
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return Object.keys(payload).length === 0
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? errorResponse("No data provided", 422)
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: {
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body: JSON.stringify({ payload }),
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statusCode: 200,
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};
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};

‎lambda-hot-reloading/lambda-typescript-webpack/src/util.ts‎

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type StringMap<T> = {
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readonly [k: string]: T[keyof T];
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};
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export function downcaseKeys<T extends Record<string, any>>(o: T): StringMap<T> {
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return Object.keys(o).reduce<StringMap<T>>((no, k) => {
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return { ...no, [k.toLowerCase()]: o[k as keyof T] };
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}, {});
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}

‎lambda-hot-reloading/lambda-typescript-webpack/tsconfig.json‎

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{
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"compilerOptions": {
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"module": "commonjs",
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"target": "es6",
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"sourceMap": false,
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"removeComments": true,
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"moduleResolution": "node",
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"strict": true,
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"strictNullChecks": true,
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"noImplicitAny": true,
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"noImplicitReturns": true,
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"noFallthroughCasesInSwitch": true,
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"noUnusedParameters": true,
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"noUnusedLocals": true,
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"lib": ["es6"],
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"allowJs": true,
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"forceConsistentCasingInFileNames": true,
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"outDir": "./dist",
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"esModuleInterop": true
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},
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"exclude": [
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"node_modules",
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"out"
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],
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"include": [
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"**/*.ts",
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"**/*.tsx"
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]
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}

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