Trix

A Rich Text Editor for Everyday Writing

Compose beautifully formatted text in your web application. Trix is a WYSIWYG editor for writing messages, comments, articles, and lists—the simple documents most web apps are made of. It features a sophisticated document model, support for embedded attachments, and outputs terse and consistent HTML.

Trix is an open-source project from 37signals, the creators of Ruby on Rails. Millions of people trust their text to us, and we built Trix to give them the best possible editing experience. See Trix in action in Basecamp 3.

Different By Design

When Trix was designed in 2014, most WYSIWYG editors were wrappers around HTML’s contenteditable and execCommand APIs, designed by Microsoft to support live editing of web pages in Internet Explorer 5.5, and eventually reverse-engineered and copied by other browsers.

Because these APIs were not fully specified or documented, and because WYSIWYG HTML editors are enormous in scope, each browser’s implementation has its own set of bugs and quirks, and JavaScript developers are left to resolve the inconsistencies.

Trix sidestepped these inconsistencies by treating contenteditable as an I/O device: when input makes its way to the editor, Trix converts that input into an editing operation on its internal document model, then re-renders that document back into the editor. This gives Trix complete control over what happens after every keystroke, and avoids the need to use execCommand at all.

This is the approach that all modern, production ready, WYSIWYG editors now take.

Built on Web standards

Trix supports all evergreen, self-updating desktop and mobile browsers.

Trix is built with established web standards, notably Custom Elements, Mutation Observer, and Promises.

Getting Started

Trix comes bundled in ESM and UMD formats and works with any asset packaging system.

The easiest way to start with Trix is including it from an npm CDN in the <head> of your page:

<head>
  …
  <link rel="stylesheet" type="text/css" href="https://unpkg.com/trix@2.0.8/dist/trix.css">
  <script type="text/javascript" src="https://unpkg.com/trix@2.0.8/dist/trix.umd.min.js"></script>
</head>

trix.css includes default styles for the Trix toolbar, editor, and attachments. Skip this file if you prefer to define these styles yourself.

Alternatively, you can install the npm package and import it in your application:

import Trix from "trix"

document.addEventListener("trix-before-initialize", () => {
  // Change Trix.config if you need
})

Creating an Editor

Place an empty <trix-editor></trix-editor> tag on the page. Trix will automatically insert a separate <trix-toolbar> before the editor.

Like an HTML <textarea>, <trix-editor> accepts autofocus and placeholder attributes. Unlike a <textarea>, <trix-editor> automatically expands vertically to fit its contents.

Integrating With Forms

To submit the contents of a <trix-editor> with a form, first define a hidden input field in the form and assign it an id. Then reference that id in the editor’s input attribute.

<form …>
  <input id="x" type="hidden" name="content">
  <trix-editor input="x"></trix-editor>
</form>

Trix will automatically update the value of the hidden input field with each change to the editor.

Populating With Stored Content

To populate a <trix-editor> with stored content, include that content in the associated input element’s value attribute.

<form …>
  <input id="x" value="Editor content goes here" type="hidden" name="content">
  <trix-editor input="x"></trix-editor>
</form>

Always use an associated input element to safely populate an editor. Trix won’t load any HTML content inside a <trix-editor>…</trix-editor> tag.

Styling Formatted Content

To ensure what you see when you edit is what you see when you save, use a CSS class name to scope styles for Trix formatted content. Apply this class name to your <trix-editor> element, and to a containing element when you render stored Trix content for display in your application.

<trix-editor class="trix-content"></trix-editor>

<div class="trix-content">Stored content here</div>

The default trix.css file includes styles for basic formatted content—including bulleted and numbered lists, code blocks, and block quotes—under the class name trix-content. We encourage you to use these styles as a starting point by copying them into your application’s CSS with a different class name.

Storing Attached Files

Trix automatically accepts files dragged or pasted into an editor and inserts them as attachments in the document. Each attachment is considered pending until you store it remotely and provide Trix with a permanent URL.

To store attachments, listen for the trix-attachment-add event. Upload the attached files with XMLHttpRequest yourself and set the attachment’s URL attribute upon completion. See the attachment example for detailed information.

If you don’t want to accept dropped or pasted files, call preventDefault() on the trix-file-accept event, which Trix dispatches just before the trix-attachment-add event.

Editing Text Programmatically

You can manipulate a Trix editor programmatically through the Trix.Editor interface, available on each <trix-editor> element through its editor property.

var element = document.querySelector("trix-editor")
element.editor  // is a Trix.Editor instance

Understanding the Document Model

The formatted content of a Trix editor is known as a document, and is represented as an instance of the Trix.Document class. To get the editor’s current document, use the editor.getDocument method.

element.editor.getDocument()  // is a Trix.Document instance

You can convert a document to an unformatted JavaScript string with the document.toString method.

var document = element.editor.getDocument()
document.toString()  // is a JavaScript string

Immutability and Equality

Documents are immutable values. Each change you make in an editor replaces the previous document with a new document. Capturing a snapshot of the editor’s content is as simple as keeping a reference to its document, since that document will never change over time. (This is how Trix implements undo.)

To compare two documents for equality, use the document.isEqualTo method.

var document = element.editor.getDocument()
document.isEqualTo(element.editor.getDocument())  // true

Getting and Setting the Selection

Trix documents are structured as sequences of individually addressable characters. The index of one character in a document is called a position, and a start and end position together make up a range.

To get the editor’s current selection, use the editor.getSelectedRange method, which returns a two-element array containing the start and end positions.

element.editor.getSelectedRange()  // [0, 0]

You can set the editor’s current selection by passing a range array to the editor.setSelectedRange method.

// Select the first character in the document
element.editor.setSelectedRange([0, 1])

Collapsed Selections

When the start and end positions of a range are equal, the range is said to be collapsed. In the editor, a collapsed selection appears as a blinking cursor rather than a highlighted span of text.

For convenience, the following calls to setSelectedRange are equivalent when working with collapsed selections:

element.editor.setSelectedRange(1)
element.editor.setSelectedRange([1])
element.editor.setSelectedRange([1, 1])

Directional Movement

To programmatically move the cursor or selection through the document, call the editor.moveCursorInDirection or editor.expandSelectionInDirection methods with a direction argument. The direction can be either "forward" or "backward".

// Move the cursor backward one character
element.editor.moveCursorInDirection("backward")

// Expand the end of the selection forward by one character
element.editor.expandSelectionInDirection("forward")

Converting Positions to Pixel Offsets

Sometimes you need to know the x and y coordinates of a character at a given position in the editor. For example, you might want to absolutely position a pop-up menu element below the editor’s cursor.

Call the editor.getClientRectAtPosition method with a position argument to get a DOMRect instance representing the left and top offsets, width, and height of the character at the given position.

var rect = element.editor.getClientRectAtPosition(0)
[rect.left, rect.top]  // [17, 49]

Inserting and Deleting Text

The editor interface provides methods for inserting, replacing, and deleting text at the current selection.

To insert or replace text, begin by setting the selected range, then call one of the insertion methods below. Trix will first remove any selected text, then insert the new text at the start position of the selected range.

Inserting Plain Text

To insert unformatted text into the document, call the editor.insertString method.

// Insert “Hello” at the beginning of the document
element.editor.setSelectedRange([0, 0])
element.editor.insertString("Hello")

Inserting HTML

To insert HTML into the document, call the editor.insertHTML method. Trix will first convert the HTML into its internal document model. During this conversion, any formatting that cannot be represented in a Trix document will be lost.

// Insert a bold “Hello” at the beginning of the document
element.editor.setSelectedRange([0, 0])
element.editor.insertHTML("<strong>Hello</strong>")

Inserting a File

To insert a DOM File object into the document, call the editor.insertFile method. Trix will insert a pending attachment for the file as if you had dragged and dropped it onto the editor.

// Insert the selected file from the first file input element
var file = document.querySelector("input[type=file]").file
element.editor.insertFile(file)

Inserting a Content Attachment

Content attachments are self-contained units of HTML that behave like files in the editor. They can be moved or removed, but not edited directly, and are represented by a single character position in the document model.

To insert HTML as an attachment, create a Trix.Attachment with a content attribute and call the editor.insertAttachment method. The HTML inside a content attachment is not subject to Trix’s document conversion rules and will be rendered as-is.

var attachment = new Trix.Attachment({ content: '<span class="mention">@trix</span>' })
element.editor.insertAttachment(attachment)

Inserting a Line Break

To insert a line break, call the editor.insertLineBreak method, which is functionally equivalent to pressing the return key.

// Insert “Hello\n”
element.editor.insertString("Hello")
element.editor.insertLineBreak()

Deleting Text

If the current selection is collapsed, you can simulate deleting text before or after the cursor with the editor.deleteInDirection method.

// “Backspace” the first character in the document
element.editor.setSelectedRange([1, 1])
element.editor.deleteInDirection("backward")

// Delete the second character in the document
element.editor.setSelectedRange([1, 1])
element.editor.deleteInDirection("forward")

To delete a range of text, first set the selected range, then call editor.deleteInDirection with either direction as the argument.

// Delete the first five characters
element.editor.setSelectedRange([0, 4])
element.editor.deleteInDirection("forward")

Working With Attributes and Nesting

Trix represents formatting as sets of attributes applied across ranges of a document.

By default, Trix supports the inline attributes bold, italic, href, and strike, and the block-level attributes heading1, quote, code, bullet, and number.

Applying Formatting

To apply formatting to the current selection, use the editor.activateAttribute method.

element.editor.insertString("Hello")
element.editor.setSelectedRange([0, 5])
element.editor.activateAttribute("bold")

To set the href attribute, pass a URL as the second argument to editor.activateAttribute.

element.editor.insertString("Trix")
element.editor.setSelectedRange([0, 4])
element.editor.activateAttribute("href", "https://trix-editor.org/")

Removing Formatting

Use the editor.deactivateAttribute method to remove formatting from a selection.

element.editor.setSelectedRange([2, 4])
element.editor.deactivateAttribute("bold")

Formatting With a Collapsed Selection

If you activate or deactivate attributes when the selection is collapsed, your formatting changes will apply to the text inserted by any subsequent calls to editor.insertString.

element.editor.activateAttribute("italic")
element.editor.insertString("This is italic")

Adjusting the Nesting Level

To adjust the nesting level of quotes, bulleted lists, or numbered lists, call the editor.increaseNestingLevel and editor.decreaseNestingLevel methods.

element.editor.activateAttribute("quote")
element.editor.increaseNestingLevel()
element.editor.decreaseNestingLevel()

Using Undo and Redo

Trix editors support unlimited undo and redo. Successive typing and formatting changes are consolidated together at five-second intervals; all other input changes are recorded individually in undo history.

Call the editor.undo and editor.redo methods to perform an undo or redo operation.

element.editor.undo()
element.editor.redo()

Changes you make through the editor interface will not automatically record undo entries. You can save your own undo entries by calling the editor.recordUndoEntry method with a description argument.

element.editor.recordUndoEntry("Insert Text")
element.editor.insertString("Hello")

Loading and Saving Editor State

Serialize an editor’s state with JSON.stringify and restore saved state with the editor.loadJSON method. The serialized state includes the document and current selection, but does not include undo history.

// Save editor state to local storage
localStorage["editorState"] = JSON.stringify(element.editor)

// Restore editor state from local storage
element.editor.loadJSON(JSON.parse(localStorage["editorState"]))

Observing Editor Changes

The <trix-editor> element emits several events which you can use to observe and respond to changes in editor state.

trix-before-initialize fires when the <trix-editor> element is attached to the DOM just before Trix installs its editor object. If you need to use a custom Trix configuration you can change Trix.config here.
trix-initialize fires when the <trix-editor> element is attached to the DOM and its editor object is ready for use.
trix-change fires whenever the editor’s contents have changed.
trix-paste fires whenever text is pasted into the editor. The paste property on the event contains the pasted string or html, and the range of the inserted text.
trix-selection-change fires any time the selected range changes in the editor.
trix-focus and trix-blur fire when the editor gains or loses focus, respectively.
trix-file-accept fires when a file is dropped or inserted into the editor. You can access the DOM File object through the file property on the event. Call preventDefault on the event to prevent attaching the file to the document.
trix-attachment-add fires after an attachment is added to the document. You can access the Trix attachment object through the attachment property on the event. If the attachment object has a file property, you should store this file remotely and set the attachment’s URL attribute. See the attachment example for detailed information.
trix-attachment-remove fires when an attachment is removed from the document. You can access the Trix attachment object through the attachment property on the event. You may wish to use this event to clean up remotely stored files.

Contributing to Trix

Trix is open-source software, freely distributable under the terms of an MIT-style license. The source code is hosted on GitHub.

We welcome contributions in the form of bug reports, pull requests, or thoughtful discussions in the GitHub issue tracker. Please see the Code of Conduct for our pledge to contributors.

Trix was created by Javan Makhmali and Sam Stephenson, with development sponsored by 37signals.

Building From Source

Trix uses Yarn to manage dependencies and Rollup to bundle its source.

Install development dependencies with:

$ yarn install

To generate distribution files run:

$ yarn build

Developing In-Browser

You can run a watch process to automatically generate distribution files when your source file change:

$ yarn watch

When the watch process is running you can run a web server to serve the compiled assets:

$ yarn dev

With the development server running, you can visit /index.html to see a Trix debugger inspector, or /test.html to run the tests on a browser.

For easier development, you can watch for changes to the JavaScript and style files, and serve the results in a browser, with a single command:

$ yarn start

Running Tests

You can also run the test in a headless mode with:

$ yarn test

// Move the cursor backward one character element.editor.moveCursorInDirection("backward") // Expand the end of the selection forward by one character element.editor.expandSelectionInDirection("forward")

// “Backspace” the first character in the document element.editor.setSelectedRange([1, 1]) element.editor.deleteInDirection("backward") // Delete the second character in the document element.editor.setSelectedRange([1, 1]) element.editor.deleteInDirection("forward")

// Save editor state to local storage localStorage["editorState"] = JSON.stringify(element.editor) // Restore editor state from local storage element.editor.loadJSON(JSON.parse(localStorage["editorState"]))