var targetNode = document.getElementById('messages');

// Options for the observer (which mutations to observe)
var config = { attributes: true, childList: true, subtree: true };

// Callback function to execute when mutations are observed
var callback = function(mutationsList) {

$( "#messages tr:contains('慢慢洗')" ).css( "display", "none" );

};

// Create an observer instance linked to the callback function
var observer = new MutationObserver(callback);

// Start observing the target node for configured mutations
observer.observe(targetNode, config);