skills/figma-generate-library/scripts/createVariableCollection.js

/**
 * createVariableCollection
 *
 * Creates a new Figma variable collection with the specified name and modes.
 * If `modeNames` has more than one entry, the first mode is renamed from
 * Figma's default "Mode 1" to the first name, and additional modes are added.
 *
 * @param {string} name - The display name of the collection (e.g. "Color", "Spacing").
 * @param {string[]} modeNames - Ordered list of mode names (e.g. ["Light", "Dark"] or ["Value"]).
 * @returns {Promise<{
 *   collection: VariableCollection,
 *   modeIds: Record<string, string>
 * }>}
 *   `modeIds` maps each mode name to its modeId string.
 */
async function createVariableCollection(name, modeNames) {
  if (!modeNames || modeNames.length === 0) {
    throw new Error('createVariableCollection: modeNames must have at least one entry.')
  }

  // Create the collection — Figma always creates it with one mode named "Mode 1".
  const collection = figma.variables.createVariableCollection(name)

  // modeIds accumulator
  const modeIds = {}

  // Rename the default first mode
  const defaultMode = collection.modes[0]
  collection.renameMode(defaultMode.modeId, modeNames[0])
  modeIds[modeNames[0]] = defaultMode.modeId

  // Add additional modes
  for (let i = 1; i < modeNames.length; i++) {
    const newModeId = collection.addMode(modeNames[i])
    modeIds[modeNames[i]] = newModeId
  }

  return { collection, modeIds }
}