function findCoupledChild(vnode) {
  var vm = vnode.child;

  if (vm) {
    if (vm.$_couplingProxy) {
      return vm;
    } else {
      return findCoupledChildInChildren(_toConsumableArray(vm.$children));
    }
  }
} // Breadth-first search
Hook called when an operation is processed. It will intelligently activate a child if needed.
@param {string} operation Name of the operation. Can be 'add' or 'remove'
@param {number} index Index of the related child.
@param {object} proxyVm Related child Vue instance