@wordpress/core-data/build-module/utils/conservative-map-item.js

Access to and manipulation of core WordPress entities.

/**
 * External dependencies
 */
import fastDeepEqual from 'fast-deep-equal/es6';

/**
 * Given the current and next item entity record, returns the minimally "modified"
 * result of the next item, preferring value references from the original item
 * if equal. If all values match, the original item is returned.
 *
 * @param {Object} item     Original item.
 * @param {Object} nextItem Next item.
 *
 * @return {Object} Minimally modified merged item.
 */
export default function conservativeMapItem(item, nextItem) {
  // Return next item in its entirety if there is no original item.
  if (!item) {
    return nextItem;
  }
  let hasChanges = false;
  const result = {};
  for (const key in nextItem) {
    if (fastDeepEqual(item[key], nextItem[key])) {
      result[key] = item[key];
    } else {
      hasChanges = true;
      result[key] = nextItem[key];
    }
  }
  if (!hasChanges) {
    return item;
  }

  // Only at this point, backfill properties from the original item which
  // weren't explicitly set into the result above. This is an optimization
  // to allow `hasChanges` to return early.
  for (const key in item) {
    if (!result.hasOwnProperty(key)) {
      result[key] = item[key];
    }
  }
  return result;
}
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