Configuring utilities for the APPSYNC_JS runtime

AWS AppSync provides two libraries that aid in the development of resolvers with the APPSYNC_JS runtime:

• @aws-appsync/eslint-plugin - Catches and fixes problems quickly during development.

• @aws-appsync/utils - Provides type validation and autocompletion in code editors.

Configuring the eslint plugin

ESLint is a tool that statically analyzes your code to quickly find problems. You can run ESLint as part of your continuous integration pipeline. @aws-appsync/eslint-plugin is an ESLint plugin that catches invalid syntax in your code when leveraging the APPSYNC_JS runtime. The plugin allows you to quickly get feedback about your code during development without having to push your changes to the cloud.

@aws-appsync/eslint-plugin provides two rule sets that you can use during development.

"plugin:@aws-appsync/base" configures a base set of rules that you can leverage in your project:

Rule	Description
no-async	Async processes and promises are not supported.
no-await	Async processes and promises are not supported.
no-classes	Classes are not supported.
no-for	for is not supported (except for for-in and for-of, which are supported)
no-continue	continue is not supported.
no-generators	Generators are not supported.
no-yield	yield is not supported.
no-labels	Labels are not supported.
no-this	this keyword is not supported.
no-try	Try/catch structure is not supported.
no-while	While loops are not supported.
no-disallowed-unary-operators	++, --, and ~ unary operators are not allowed.
no-disallowed-binary-operators	The instanceof operator is not allowed.
no-promise	Async processes and promises are not supported.

"plugin:@aws-appsync/recommended" provides some additional rules but also requires you to add TypeScript configurations to your project.

Rule	Description
no-recursion	Recursive function calls are not allowed.
no-disallowed-methods	Some methods are not allowed. See the reference for a full set of supported built-in functions.
no-function-passing	Passing functions as function arguments to functions is not allowed.
no-function-reassign	Functions cannot be reassigned.
no-function-return	Functions cannot be the return value of functions.

To add the plugin to your project, follow the installation and usage steps at Getting Started with ESLint. Then, install the plugin in your project using your project package manager (e.g., npm, yarn, or pnpm):

$ npm install @aws-appsync/eslint-plugin

In your .eslintrc.{js,yml,json} file, add "plugin:@aws-appsync/base" or "plugin:@aws-appsync/recommended" to the extends property. The snippet below is a basic sample .eslintrc configuration for JavaScript:

{
  "extends": ["plugin:@aws-appsync/base"]
}

To use the "plugin:@aws-appsync/recommended" rule set, install the required dependency:

$ npm install -D @typescript-eslint/parser

Then, create an .eslintrc.js file:

{
  "parser": "@typescript-eslint/parser",
  "parserOptions": {
    "ecmaVersion": 2018,
    "project": "./tsconfig.json"
  },
  "extends": ["plugin:@aws-appsync/recommended"]
}