// 异常	//程序抛出异常	var add = function(){		if(typeof a !== 'number' || typeof b !== 'number'){			throw{				name:'TypeError',				message:'add need number'			};		}		return a+b;	};	var  try_it = function(){		try{			add('seven')		} catch(e){			console.log(e.name + ':'+e.message);		}	}	try_it();//try出现异常，则跳转到catch从句