摘要：
/*对象和函数将秘密调用toString*/vardemo_fun=function｛console.log｝console。日志演示乐趣。toString=demo_fun.toValue=函数（）｛console.log；return'demo_fun'｝控制台。日志vardemo_obj={i:10}控制台。日志demo_obj.toString=demo_obj.toValue=函数（）｛console.log；return'demo_obj'；｝安慰日志；/*标题*/functionadd｛varres=n；varfun=函数｛res+=n；returnfun；｝fun.toString=有趣。valueOf=函数（）｛returnres｝returnfun；｝vara=添加；控制台日志；
/*对象和函数会偷偷调用toString*/
var demo_fun = function(n){ console.log('per') } console.log(demo_fun); demo_fun.toString = demo_fun.toValue = function(){ console.log('Run toString , Run toValue'); return 'demo_fun' } console.log(demo_fun); var demo_obj = { i:10 } console.log(demo_obj); demo_obj.toString = demo_obj.toValue = function(){ console.log('Run toString , Run toValue'); return 'demo_obj'; } console.log(demo_obj);
/*题目*/
function add(n){ var res = n; var fun = function(n){ res += n; return fun; } fun.toString = fun.valueOf = function(){return res} return fun; } var a = add(1)(2)(3)(4); console.log(a);