基于js实现的限制文本框只可以输入数字

function getEvent() { if (document.all) {  return window.event; //for ie } func = getEvent.caller; while (func != null) {  var arg0 = func.arguments[0];  if (arg0) {  if ((arg0.constructor == Event || arg0.constructor == MouseEvent) || (typeof (arg0) == "object" && arg0.preventDefault && arg0.stopPropagation)) {     return arg0;   }  }  func = func.caller; } return null; };  function doit(){  var ev = getEvent();  if(ev.keyCode < 8) {return false;}  else if(ev.keyCode > 8 && ev.keyCode < 48) {return false;}  else if(ev.keyCode > 57 && ev.keyCode <96) {return false;}  else if(ev.keyCode > 105) {return false;}  else {return true;} };