Javascript是否在对象中 in

$(document).ready(function() {  var triggers = {    D: 'default',    N: 'narrow',    L: 'large'  };  $(document).keyup(function(event) {    var key = String.fromCharCode(event.keyCode);    if (key in triggers) {      $('#switcher-' + triggers[key]).click();    }  });});