react dom 18.2.0
shouldComponentUpdate
1、先用object.is判断
2、在判断A和B是否是null
3、A和B的keys长度比较
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;
}
