Debug a plugin

Debug and inspect your plugin with the help of logs, Safari Web Inspector and the Sketch DevTools plugin.

Logs

Use console to log anything in JavaScript. The resulting logs can be viewed in:

  • Safari Web Inspector Console
  • macOS Console.app located in ApplicationsUtilities
  • Sketch log file ~/Library/Logs/com.bohemiancoding.sketch3/Plugin Log.log

Quick tip: If you’re using skpm run skpm log -f to stream logs on the command-line.

Safari Web Inspector

When a plugin is run, Sketch initializes a new JavaScript runtime environment for it. By default this JSContext is short-lived and destroyed once the plugin command is completed. However, it is still possible to attach the debugger provided by the Safari Web Inspector. From the submenu matching you computer name in the Develop menu, select:

  1. Automatically Show Web Inspector for JSContexts
  2. Automatically Pause Connecting to JSContexts to set breakpoints in your source code.

Enable Safari Web Inspector and Debugger

Once done with debugging you may want to deselect these options again or Safari will open the Web Inspector for any plugin run within Sketch or other applications using JSContext.

Note: The Develop menu in Safari is not shown by default. To enable it, make sure to check the Show Develop menu in menu bar option within PreferencesAdvanced.

Introspect the Objective-C runtime

Native Sketch objects are bridged from Objective-C to JavaScript. Query information about properties, class and instance methods as well as protocols using Mocha.

let mocha = context.document.class().mocha()
console.log(mocha.properties())

See the Mocha documentation for a complete list of available introspection methods.

Inspect Sketch documents with Sketch DevTools

Sketch DevTools is a Sketch plugin that lets you inspect elements within a document without writing code.

Inspect a plugin’s webview

To inspect plugin user interfaces built using a webview you need to set a user default.

defaults write com.bohemiancoding.sketch3 WebKitDeveloperExtras -bool YES

If you’re using a Beta version of Sketch make sure to use the correct application bundle identifier.

defaults write com.bohemiancoding.sketch3.beta WebKitDeveloperExtras -bool YES

DOM elements can be inspected by right-clicking inside the webview and select Inspect Element which brings up the Safari Web Inspector. If you have JavaScript code supressing the context menu you can still inspect elements by selecting them directly within Elements in Safari Web Inspector.

Note: If you’re using skpm, the WebKitDeveloperExtras user default will be set to YES automatically.

Troubleshooting

Reload scripts

By default, Sketch caches plugins for performance reasons. Changes to plugins are therefor not automatically recognized. To force Sketch to always reload a plugin before running it set the following value in the user defaults.

defaults write com.bohemiancoding.sketch3 AlwaysReloadScript -bool YES

Sketch only reloads a plugin directly before it gets invoked. For scripts using a long-running JavaScript context Sketch must be restarted. If you are still using coscript.setShouldKeepAround(false) we encourage you to instead use fibers which provide more granular control over the lifecycle of a JavaScript context.

Note: If you’re using skpm, the AlwaysReloadScript user default will be set to YES automatically.

Automatically restart Sketch after plugin changes

If your plugin uses a long-running JavaScript context it can be useful during development to restart Sketch every time a change is made. This can be done automatically using the Unix utility entr.

Install entr manually or using Homebrew.

brew install entr

Watch the plugin bundle for changes in any of the scripts and provide the path to Sketch.

find /path/to/my-plugin.sketchplugin -name '*js' | entr \
  -r /Applications/Sketch.app/Contents/MacOS/Sketch

Clear plugin cache manually

The plugin cache contains the current and previously installed versions of plugins. To clear the cache remove the folder for a specific plugin or the entire cache PluginsWarehouse from:

~/Library/Application Support/com.bohemiancoding.sketch3/PluginsWarehouse

Sketch will recreate the cache next time a plugin gets initialized.

Ensure matching version number in manifest.json and appcast

A plugin installation fails if the plugin version specified in the appcast does not match the version number in manifest.json.

Disable Safe Mode after plugin crashing Sketch

If a plugin causes Sketch to crash, Sketch uses Safe Mode by default and disables all plugins next time it’s launched. This behaviour can be disabled by setting a user default.

defaults write com.bohemiancoding.sketch3 disableAutomaticSafeMode YES

If you’re using the Beta version, you’ll need to run:

defaults write com.bohemiancoding.sketch3.beta disableAutomaticSafeMode YES

To restore the default behavior, delete the user default.

defaults delete com.bohemiancoding.sketch3 disableAutomaticSafeMode

Handle all actions

For development purposes it can be helpful to subscribe to all actions. By default Sketch only forwards actions that have been explicitely specified in the plugin manifest. Set the actionWildcardsAllowed user default to YES to forward all actions.

defaults write com.bohemiancoding.sketch3 actionWildcardsAllowed -bool YES

Update the manifest to include a generic action handler by specifying a action wildcard.

  "handlers": {
+    "actions": {
+      "*": "onAction"
+    }
  }

Note: Use wildcard action handlers for development and debugging only as they impact Sketch’ performance negatively.

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