JavaScript中判断函数、变量是否存在

function isExitsFunction(funcName) {  try {    if (typeof(eval(funcName)) == "function") {      return true;    }  } catch(e) {}  return false;}

if (typeof String.prototype.endsWith != 'function') { String.prototype.endsWith = function(suffix) {  return this.indexOf(suffix, this.length - suffix.length) !== -1; };}

try {  if(typeof(eval(funcName))=="function")  {   funcName(); }}catch(e){//alert("not function"); } 

function isExitsVariable(variableName) {  try {    if (typeof(variableName) == "undefined") {      //alert("value is undefined");       return false;    } else {      //alert("value is true");       return true;    }  } catch(e) {}  return false;}

if("undefined" != typeof downlm){ if(downlm=="soft"){ document.write('成功'); } }