export function mergeChildMappings()

in src/utils/ChildMapping.js [39:82]

• 32 lines of code
• 10 McCabe index (conditional complexity)

export function mergeChildMappings(prev, next) {
  prev = prev || {};
  next = next || {};

  function getValueForKey(key) {
    return key in next ? next[key] : prev[key];
  }

  // For each key of `next`, the list of keys to insert before that key in
  // the combined list
  let nextKeysPending = Object.create(null);

  let pendingKeys = [];
  for (let prevKey in prev) {
    if (prevKey in next) {
      if (pendingKeys.length) {
        nextKeysPending[prevKey] = pendingKeys;
        pendingKeys = [];
      }
    } else {
      pendingKeys.push(prevKey);
    }
  }

  let i;
  let childMapping = {};
  for (let nextKey in next) {
    if (nextKeysPending[nextKey]) {
      for (i = 0; i < nextKeysPending[nextKey].length; i++) {
        let pendingNextKey = nextKeysPending[nextKey][i];
        childMapping[nextKeysPending[nextKey][i]] =
          getValueForKey(pendingNextKey);
      }
    }
    childMapping[nextKey] = getValueForKey(nextKey);
  }

  // Finally, add the keys which didn't appear before any key in `next`
  for (i = 0; i < pendingKeys.length; i++) {
    childMapping[pendingKeys[i]] = getValueForKey(pendingKeys[i]);
  }

  return childMapping;
}