react dom 18.2.0
shouldComponentUpdate
1、先用object.is判斷
2、在判斷A和B是否是null
3、A和B的keys長度比較
4、A和B的key是否相同 或者 A和B的value值是否相同

function shallowEqual(objA, objB) {
  if (objectIs(objA, objB)) {
    return true;
  }

  if (typeof objA !== 'object' || objA === null || typeof objB !== 'object' || objB === null) {
    return false;
  }

  var keysA = Object.keys(objA);
  var keysB = Object.keys(objB);

  if (keysA.length !== keysB.length) {
    return false;
  } // Test for A's keys different from B.


  for (var i = 0; i < keysA.length; i++) {
    var currentKey = keysA[i];

    if (!hasOwnProperty.call(objB, currentKey) || !objectIs(objA[currentKey], objB[currentKey])) {
      return false;
    }
  }

  return true;
}