Create Sketch Assistant writing a custom rule

sketch-comic-assistant.ts

/**

  Simple Assistant setting exactly one rule that ensures text layers are only using
  specific fonts, in this case set to Comic Sans and Cochin.

  1. Use Assistant Template from https://github.com/sketch-hq/sketch-assistant-template/
  2. Find and replace all `sketch-assistant-template` with `sketch-comic-assistant`
  3. Install dependencies

    npm install

  4. Replace src/index.ts with this gist's content
  5. Create Assistant package

    npm run package-tarball

  6. Test resulting `.tgz` with your Sketch document via Assistants window › Manage Assistants… › Add from Archive…

 */

import { AssistantPackage, RuleDefinition, FileFormat } from '@sketch-hq/sketch-assistant-types'

const textFontAllowed: RuleDefinition = {
  rule: async (context) => {
    const { utils } = context
    const allowedFonts: string[] = utils.getOption('allowedFonts')

    let objects: Set<FileFormat.Text> = new Set()

    for (const text of utils.objects.text) {
      const font =
        text.style?.textStyle?.encodedAttributes.MSAttributedStringFontAttribute.attributes.name

      let pass = false
      for (const f of allowedFonts) {
        if (font?.startsWith(f)) {
          pass = true
          break
        }
      }

      if (pass) continue

      objects.add(text)
    }

    if (objects.size == 0) return

    utils.report(`${objects.size} text layers are not using ${allowedFonts.join(', ')}`, ...objects)
  },
  name: 'sketch-comic-assistant/text-font-allowed',
  title: 'Text must use Comic Sans',
  description: 'Because Comic Sans is the best font in the world.',
  getOptions: (helpers) => [
    helpers.stringArrayOption({
      name: 'allowedFonts',
      title: 'Allowed Fonts',
      description: 'The font family names that are allowed to be used.',
    }),
  ],
}

const assistant: AssistantPackage = async () => {
  return {
    name: 'sketch-comic-assistant',
    rules: [textFontAllowed],
    config: {
      rules: {
        'sketch-comic-assistant/text-font-allowed': {
          active: true,
          allowedFonts: ['ComicSans', 'Cochin'],
        },
      },
    },
  }
}
export default assistant