Object diff

diff.ts

// Adapted from https://stackoverflow.com/a/61406094/521662

export interface ObjectComparison {
  added?: Record<any, any>;
  updated?: Record<string, Change>;
  removed?: Record<any, any>;
}

export interface Change {
  oldValue: any;
  newValue: any;
}

export function diff(
  o1: Record<any, any>,
  o2: Record<any, any>,
  shallow = false
): ObjectComparison {
  const added: Record<any, any> = {};
  const updated: Record<any, any> = {};
  const removed: Record<any, any> = {};
  for (const prop in o1) {
    if (o1.hasOwnProperty(prop)) {
      const o2PropValue = o2[prop];
      const o1PropValue = o1[prop];
      if (o2.hasOwnProperty(prop)) {
        if (o2PropValue !== o1PropValue) {
          updated[prop] =
            !shallow && isObject(o1PropValue) && isObject(o2PropValue)
              ? diff(o1PropValue, o2PropValue, shallow)
              : { newValue: o2PropValue };
        }
      } else {
        removed[prop] = o1PropValue;
      }
    }
  }
  for (const prop in o2) {
    if (o2.hasOwnProperty(prop)) {
      const o1PropValue = o1[prop];
      const o2PropValue = o2[prop];
      if (o1.hasOwnProperty(prop)) {
        if (o1PropValue !== o2PropValue) {
          if (shallow || !isObject(o1PropValue)) {
            updated[prop].oldValue = o1PropValue;
          }
        }
      } else {
        added[prop] = o2PropValue;
      }
    }
  }

  let result: ObjectComparison = {};
  if (Object.keys(added).length) result.added = added;
  if (Object.keys(updated).length) result.updated = updated;
  if (Object.keys(removed).length) result.removed = removed;

  return result;
}

function isObject(o: any) {
  return o !== null && typeof o === "object";
}