# react-simple-code-editor

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Simple no-frills code editor with syntax highlighting.

<a href="https://raw.githubusercontent.com/satya164/react-simple-code-editor/master/demo/demo.gif"><img src="https://raw.githubusercontent.com/satya164/react-simple-code-editor/master/demo/demo.gif" width="400"></a>

## Why

Several browser based code editors such as Ace, CodeMirror, Monaco etc. provide the ability to embed a full-featured code editor in your web page. However, if you just need a simple editor with syntax highlighting without any of the extra features, they can be overkill as they don't usually have a small bundle size footprint. This library aims to provide a simple code editor with syntax highlighting support without any of the extra features, perfect for simple embeds and forms where users can submit code.

## Features

- Modular syntax highlighting with third party library
- Indent line or selected text by pressing tab key, with customizable indentation
- Automatic indent on new lines
- Wrap selected text in parens, brackets, or quotes
- Undo whole words instead of letter by letter
- Accessible, use `Ctrl+Shift+M` (Mac) / `Ctrl+M` to toggle capturing tab key

## Installation

```sh
npm install react-simple-code-editor
```

or

```sh
yarn add react-simple-code-editor
```

## Usage

You need to use the editor with a third party library which provides syntax highlighting. For example, it'll look like following with [`prismjs`](https://prismjs.com):

```js
import React from 'react';
import Editor from 'react-simple-code-editor';
import { highlight, languages } from 'prismjs/components/prism-core';
import 'prismjs/components/prism-clike';
import 'prismjs/components/prism-javascript';

const code = `function add(a, b) {
  return a + b;
}
`;

class App extends React.Component {
  state = { code };

  render() {
    return (
      <Editor
        value={this.state.code}
        onValueChange={code => this.setState({ code })}
        highlight={code => highlight(code, languages.js)}
        padding={10}
        style={{
          fontFamily: '"Fira code", "Fira Mono", monospace',
          fontSize: 12,
        }}
      />
    );
  }
}
```

Note that depending on your syntax highlighter, you might have to include additional CSS for syntax highlighting to work.

## Props

The editor accepts all the props accepted by `textarea`. In addition, you can pass the following props:

- `value` (`string`): Current value of the editor i.e. the code to display. This must be a [controlled prop](https://reactjs.org/docs/forms.html#controlled-components).
- `onValueChange` (`string => mixed`): Callback which is called when the value of the editor changes. You'll need to update the value prop when this is called.
- `highlight` (`string => string | React.Node`): Callback which will receive text to highlight. You'll need to return an HTML string or a React element with syntax highlighting using a library such as [`prismjs`](https://prismjs.com).
- `tabSize` (`number`): The number of characters to insert when pressing tab key. For example, for 4 space indentation, `tabSize` will be `4` and `insertSpaces` will be `true`. Default: `2`.
- `insertSpaces` (`boolean`): Whether to use spaces for indentation. Default: `true`. If you set it to `false`, you might also want to set `tabSize` to `1`.
- `ignoreTabKey` (`boolean`): Whether the editor should ignore tab key presses so that keyboard users can tab past the editor. Users can toggle this behaviour using `Ctrl+Shift+M` (Mac) / `Ctrl+M` manually when this is `false`. Default: `false`.
- `padding` (`number`): Optional padding for code. Default: `0`.
- `textareaId` (`string`): An ID for the underlying `textarea`, can be useful for setting a `label`.

## Demo

[satya164.github.io/react-simple-code-editor](https://satya164.github.io/react-simple-code-editor)

## How it works

It works by overlaying a syntax highlighted `<pre>` block over a `<textarea>`. When you type, select, copy text etc., you interact with the underlying `<textarea>`, so the experience feels native. This is a very simple approach compared to other editors which re-implement the behaviour.

The syntax highlighting can be done by any third party library as long as it returns HTML and is fully controllable by the user.

The vanilla `<textarea>` doesn't support inserting tab characters for indentation, so we re-implement it by listening to `keydown` events and programmatically updating the text. One caveat with programmatically updating the text is that we lose the undo stack, so we need to maintain our own undo stack. As a result, we can also implement improved undo behaviour such as undoing whole words similar to editors like VSCode.

## Limitations

Due to the way it works, it has certain limitations:

- The syntax highlighted code cannot have different font family, font weight, font style, line height etc. for its content. Since the editor works by aligning the highlighted code over a `<textarea>`, changing anything that affects the layout can misalign it.
- The custom undo stack is incompatible with undo/redo items browser's context menu. However, other full featured editors don't support browser's undo/redo menu items either.
- The editor is not optimized for performance and large documents can affect the typing speed.
- We hide text in the textarea using `-webkit-text-fill-color: transparent`, which works in all modern browsers (even non-webkit ones such as Firefox and Edge). On IE 10+, we use `color: transparent` which doesn't hide the cursor. Text may appear bolder in unsupported browsers.

## Contributing

While developing, you can run the example app to test your changes:

```sh
yarn example
```

Make sure your code passes Flow and ESLint. Run the following to verify:

```sh
yarn flow
yarn lint
```

To fix formatting errors, run the following:

```sh
yarn lint -- --fix
```

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