Messenger Preview 0.1 CRX for Chrome

▶ Update:

This extension no longer works as of December 16th, 2020. Messenger made extensive changes to their user interface, including disabling KaTeX. Since the KaTeX preview was my main motivation for making this, I have no intentions to fix this extension.

However, the number of users has tripled (~30 to 100) since it broke, so I'm leaving this published on the off-chance that it still works for some people.

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Messenger has many different formatting options, such as bold, italics, strikethrough, monospaced code, and math formatting through KaTeX (a subset of LaTeX). It can be hard to know what a message will look like without sending it once, so this extension shows a preview of how each message will appear before you send it.

Note: the formatting only renders properly on web Messenger. Mobile Messenger does not show any of the formatting.

All previews are performed client-side. None of your information is sent to any third-party server.

See https://www.facebook.com/help/147348452522644 for details on formatting text.

Supported functions in the LaTeX math formatting are at https://www.facebook.com/help/147348452522644.

▶ Usage

Write messages as normal. As you type, you should see a light message appear about where it will appear when you send the message (when it actually sends, your message might attach to the group above it). Sometimes, the preview is a bit hidden, requiring you to scroll down within the chat.

Warning: Sometimes the preview does not show at first. Reload the messenger page once, and it should appear at least until you open another conversation. Reloading the page does *not* delete the contents of the message box.

As usual in Messenger chats, write

• *bold*
• _italics_
• ~strikethrough~
• \(\) to display inline math using LaTeX, e.g. `\(\frac{1}{2}\)`
• \[\] to display math that takes up the whole message. This may include
scrollbars and is useful for long chunks of math.
• `inline code`
• ```full message code```
• for code with syntax highlighting, use

```python
def f(a,b):
return a + b
```

If necessary, press ctrl+enter to create a newline within a message.

The math uses a subset of KaTeX, which is itself a subset of LaTeX. See the
[Katex Docs](https://katex.org/docs/supported.html) for supported functions.
Some functions only work within math that takes up the whole message
(`\[...\]`). If anything at all is wrong, none of the message will render as
math.

Clicking the three dots to the left of a message then "Show Original" will
remove all formatting from the message.

▶ Limitations
This is an unofficial extension; Facebook might change Messenger at any time which could break this extension.

The extension only works in www.messenger.com and www.facebook.com/messenger, not the preview within www.facebook.com.