Document changes

Listen to arbitrary changes in a Sketch document using the onDocumentChange handler. It provides a mechanism to listen to three types of fundamental change events in documents – changes, removals and additions.

This API is available starting with Sketch 59 and is designed as a scalable and more flexible replacement for Actions that handle specific document changes.

🚧 We’re releasing this feature early to gather feedback from the community, so the API may change in future. Let us know what you think, file an issue for comments, suggestions and bug reports or send an email to developer@sketch.com.

🚀 Check the document-change-sketchplugin for an example implementation, or keep reading for a quick introduction.

Change types

The fundamental document change types are:

  • Property changes, e.g. a layer’s x/y position changing
  • Object addition, e.g. adding a new layer to the canvas
  • Object removal, e.g. deleting a layer

Note that an object moving around within the layer hierarchy is removed from the previous path and re-added at a new path - such changes have their isMove flag set to true. See the code examples below for more information.

Manifest handler

Subscribe to changes via the new onDocumentChanged handler defined in the plugin manifest.

{
  "compatibleVersion": 3,
  "bundleVersion": 1,
  "identifier": "com.sketch.plugins.document-change-example",
  "commands": [
    {
      "script": "command.js",
      "handlers": {
        "onDocumentChanged": "onDocumentChanged"
      }
    }
  ],
  "version": "1.0.0",
  "name": "Document Change",
  "description": "Sample plugin showcasing how to handle document changes such as object addition, deletions and modifications.",
  "author": "Sketch",
  "disableCocoaScriptPreprocessor": true
}

Handler definition

Similarly to existing handlers, a JavaScript function needs to be defined to handle incoming document change events. The function is called repeatedly by Sketch while the document is being changed.

Changes that happen in quick succession may be batched, therefore your handler will receive an argument containing a set of changes.

function onDocumentChanged(context) {
  var changes = context.actionContext
  for (var i = 0; i < changes.length; i++) {
    var change = changes[i]
    var path = change.fullPath() // Path to the affected object or property
    var type = change.type() // Change type, see example below for values
    var obj = change.object() // Reference to the mutable object
    var isMove = change.isMove() // Whether addition/removal is associated with a move
  }
}

The following boilerplate illustrates one way to handle each of the change types, including a move.

function onDocumentChanged(context) {
  var changes = context.actionContext

  for (var i = 0; i < changes.length; i++) {
    var change = changes[i]
    var type = change.type()
    var isMove = change.isMove()
    switch (type) {
      case 1:
        // Handle property change
        break
      case 2:
        if (!isMove) {
          // Handle deletion
        }
        break
      case 3:
        if (isMove) {
          // Handle move
        } else {
          // Handle addition
        }
        break
    }
  }
}
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