我有一个函数，当用户在输入字段中输入5个字符时会触发该函数。
然而，每当我放置额外的字符后，5已履行它不断发射的事件。
如何防止这种情况发生？

$(function(){
    var $zipEntry = $('#zipEntry').bind('keyup',function(event) { //bind to key up, doesn't require 
    //make sure that there are 5 numbers... or length = 5 since numeric only input
    var $this = $(this); // cache $(this)
    
        if ($this.val().length == 5){ // use cached 
            console.log("There are 5 characters!!");
            $this.trigger('zipEntered'); 
        }
    });