LitElement TypeScript starter

This project includes a sample component using LitElement with TypeScript.

Setup

Install dependencies:

npm i

Build

This sample uses the TypeScript compiler to produce JavaScript that runs in modern browsers.

To build the JavaScript version of your component:

npm run build

To watch files and rebuild when the files are modified, run the following command in a separate shell:

npm run build:watch

Both the TypeScript compiler and lit-analyzer are configured to be very strict. You may want to change tsconfig.json to make them less strict.

Testing

This sample uses Karma, Chai, Mocha, and the open-wc test helpers for testing. See the open-wc testing documentation for more information.

Tests can be run with the test script:

npm test

Dev Server

This sample uses open-wc's es-dev-server for previewing the project without additional build steps. ES dev server handles resolving Node-style "bare" import specifiers, which aren't supported in browsers. It also automatically transpiles JavaScript and adds polyfills to support older browsers.

To run the dev server and open the project in a new browser tab:

npm run serve

Editing

If you use VS Code, we highly reccomend the lit-plugin extension, which enables some extremely useful features for lit-html templates:

Syntax highlighting
Type-checking
Code completion
Hover-over docs
Jump to definition
Linting
Quick Fixes

The project is setup to reccomend lit-plugin to VS Code users if they don't already have it installed.

Linting

Linting of TypeScript files is provided by ESLint and TypeScript ESLint. In addition, lit-analyzer is used to type-check and lint lit-html templates with the same engine and rules as lit-plugin.

The rules are mostly the recommended rules from each project, but some have been turned off to make LitElement usage easier. The recommended rules are pretty strict, so you may want to relax them by editing .eslintrc.json and tsconfig.json.

To lint the project run:

npm run lint

Formatting

Prettier is used for code formatting. It has been pre-configured according to the Polymer Project's style. You can change this in .prettierrc.json.

Prettier has not been configured to run when commiting files, but this can be added with Husky and and pretty-quick. See the prettier.io site for instructions.

More information

See Get started on the LitElement site for more information.

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