js柯里化

function sum(x){console.log('x:='+x);var y = function(x){ console.log('xx:='+x);console.log('y:='+y);return sum(x+y) }y.toString = y.valueOf = function(){ return x; } console.log('yy:='+y);return y; 
} 
sum(1)(2)(3)(4);//10