## react-native-viewport-helpers

### Install

`yarn add react-native-viewport-helpers` or `npn install react-native-viewport-helpers`

## Usage

Works like a regular useLayoutEffect hook.

Takes in a `ref`from `useRef`. An `effect function` that works just like useEffect meaning a cleanup can be returned. `Dependencies` for the effect, and a `delay` that is by default 500ms.

This works through polling, so it's not the most performance friendly thing, but it works.

```js
import * as React from 'react';
import { useIsInViewPortEffect } from 'react-native-viewport-helpers';
import { useRef } from 'react';
import { View, Text, ScrollView } from 'react-native';

const App = () => {
  const arr = new Array(100).fill(1);
  return (
    <ScrollView>
      {arr.map((e, i) => (
        <div key={`key${i}`}>{i}</div>
      ))}
      <Component />
      {arr.map((e, i) => (
        <div key={`key${i}`}>{i}</div>
      ))}
    </ScrollView>
  );
};

const Component = () => {
  const ref = useRef < any > null;
  useIsInViewPortEffect(
    ref,
    () => {
      console.log('Hello World');
      return () => {
        console.log('goodbye!');
      };
    },
    [],
    2000
  );
  return (
    <View ref={ref}>
      <Text>Hello</Text>
    </View>
  );
};
```

## TSDX

This was made with TSDX + a few changes, readme for that below

### Commands

TSDX scaffolds your new library inside `/src`, and also sets up a [Parcel-based](https://parceljs.org) playground for it inside `/example`.

The recommended workflow is to run TSDX in one terminal:

```
npm start # or yarn start
```

This builds to `/dist` and runs the project in watch mode so any edits you save inside `src` causes a rebuild to `/dist`.

Then run the example inside another:

```
cd example
npm i # or yarn to install dependencies
npm start # or yarn start
```

The default example imports and live reloads whatever is in `/dist`, so if you are seeing an out of date component, make sure TSDX is running in watch mode like we recommend above. **No symlinking required**, [we use Parcel's aliasing](https://github.com/palmerhq/tsdx/pull/88/files).

To do a one-off build, use `npm run build` or `yarn build`.

To run tests, use `npm test` or `yarn test`.

### Configuration

Code quality is [set up for you](https://github.com/palmerhq/tsdx/pull/45/files) with `prettier`, `husky`, and `lint-staged`. Adjust the respective fields in `package.json` accordingly.

#### Jest

Jest tests are set up to run with `npm test` or `yarn test`. This runs the test watcher (Jest) in an interactive mode. By default, runs tests related to files changed since the last commit.

###### Setup Files

This is the folder structure we set up for you:

```
/example
  index.html
  index.tsx       # test your component here in a demo app
  package.json
  tsconfig.json
/src
  index.tsx       # EDIT THIS
/test
  blah.test.tsx   # EDIT THIS
.gitignore
package.json
README.md         # EDIT THIS
tsconfig.json
```

###### React Testing Library

We do not set up `react-testing-library` for you yet, we welcome contributions and documentation on this.

#### Rollup

TSDX uses [Rollup v1.x](https://rollupjs.org) as a bundler and generates multiple rollup configs for various module formats and build settings. See [Optimizations](#optimizations) for details.

#### TypeScript

`tsconfig.json` is set up to interpret `dom` and `esnext` types, as well as `react` for `jsx`. Adjust according to your needs.

### Continuous Integration

#### Travis

_to be completed_

#### Circle

_to be completed_

### Optimizations

Please see the main `tsdx` [optimizations docs](https://github.com/palmerhq/tsdx#optimizations). In particular, know that you can take advantage of development-only optimizations:

```js
// ./types/index.d.ts
declare var __DEV__: boolean;

// inside your code...
if (__DEV__) {
  console.log('foo');
}
```

You can also choose to install and use [invariant](https://github.com/palmerhq/tsdx#invariant) and [warning](https://github.com/palmerhq/tsdx#warning) functions.

### Module Formats

CJS, ESModules, and UMD module formats are supported.

The appropriate paths are configured in `package.json` and `dist/index.js` accordingly. Please report if any issues are found.

### Using the Playground

```
cd example
npm i # or yarn to install dependencies
npm start # or yarn start
```

The default example imports and live reloads whatever is in `/dist`, so if you are seeing an out of date component, make sure TSDX is running in watch mode like we recommend above. **No symlinking required**!

### Deploying the Playground

The Playground is just a simple [Parcel](https://parceljs.org) app, you can deploy it anywhere you would normally deploy that. Here are some guidelines for **manually** deploying with the Netlify CLI (`npm i -g netlify-cli`):

```bash
cd example # if not already in the example folder
npm run build # builds to dist
netlify deploy # deploy the dist folder
```

Alternatively, if you already have a git repo connected, you can set up continuous deployment with Netlify:

```bash
netlify init
# build command: cd example && yarn && yarn build
# directory to deploy: example/dist
# pick yes for netlify.toml
```

### Named Exports

Per Palmer Group guidelines, [always use named exports.](https://github.com/palmerhq/typescript#exports) Code split inside your React app instead of your React library.

### Including Styles

There are many ways to ship styles, including with CSS-in-JS. TSDX has no opinion on this, configure how you like.

For vanilla CSS, you can include it at the root directory and add it to the `files` section in your `package.json`, so that it can be imported separately by your users and run through their bundler's loader.

### Publishing to NPM

We recommend using https://github.com/sindresorhus/np.

### Usage with Lerna

When creating a new package with TSDX within a project set up with Lerna, you might encounter a `Cannot resolve dependency` error when trying to run the `example` project. To fix that you will need to make changes to the `package.json` file _inside the `example` directory_.

The problem is that due to the nature of how dependencies are installed in Lerna projects, the aliases in the example project's `package.json` might not point to the right place, as those dependencies might have been installed in the root of your Lerna project.

Change the `alias` to point to where those packages are actually installed. This depends on the directory structure of your Lerna project, so the actual path might be different from the diff below.

```diff
   "alias": {
-    "react": "../node_modules/react",
-    "react-dom": "../node_modules/react-dom"
+    "react": "../../../node_modules/react",
+    "react-dom": "../../../node_modules/react-dom"
   },
```

An alternative to fixing this problem would be to remove aliases altogether and define the dependencies referenced as aliases as dev dependencies instead. [However, that might cause other problems.](https://github.com/palmerhq/tsdx/issues/64)