$delete 源码与删除逻辑

function del (target, key) {
    if (
      (isUndef(target) || isPrimitive(target))
    ) {
      warn(("Cannot delete reactive property on undefined, null, or primitive value: " + ((target))));
    }
    if (Array.isArray(target) && isValidArrayIndex(key)) {
      target.splice(key, 1);
      return
    }
    var ob = (target).__ob__;
    if (target._isVue || (ob && ob.vmCount)) {
       warn(
        'Avoid deleting properties on a Vue instance or its root $data ' +
        '- just set it to null.'
      );
      return
    }
    if (!hasOwn(target, key)) {
      return
    }
    delete target[key];
    if (!ob) {
      return
    }
    ob.dep.notify();
}

如果是对象就是 delete target[key] ,如果是数组则target.splice(key, 1);