Mailspring/docs/ComposerExtensions.md

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---
Title: Extending the Composer
Section: Guides
Order: 6
---
The composer lies at the heart of N1, and many improvements to the mail experience require deep integration with the composer. To enable these sort of plugins, the {DraftStore} exposes an extension API.
This API allows your package to:
- Display warning messages before a draft is sent. (ie: "Are you sure you want to send this without attaching a file?")
- Intercept keyboard and mouse events to the composer's text editor.
- Transform the draft and make additional changes before it is sent.
To create your own composer extensions, subclass {ComposerExtension} and override the methods your extension needs.
In the sample packages repository, [templates]() is an example of a package which uses a ComposerExtension to enhance the composer experience.
### Example
This extension displays a warning before sending a draft that contains the names of competitors' products. If the user proceeds to send the draft containing the words, it appends a disclaimer.
```coffee
{ComposerExtension} = require 'nylas-exports'
class ProductsExtension extends ComposerExtension
@warningsForSending: ({draft}) ->
words = ['acme', 'anvil', 'tunnel', 'rocket', 'dynamite']
body = draft.body.toLowercase()
for word in words
if body.indexOf(word) > 0
return ["with the word '#{word}'?"]
return []
@applyTransformsForSending: ({draftBodyRootNode, draft}) ->
if @warningsForSending({draft})
el = document.createElement('p');
el.innerText = "This email contains competitor's product names or trademarks used in context."
draftBodyRootNode.appendChild(el)
```