var numberObject=new Number(1333);numberObject.valueOf();

1333

var numberObject=new Number(1333);numberObject.toExponential(3);

"1.333e+3"

undefined

var numberObject=new Number(1333);numberObject.toFixed(2);

"1333.00"

var numberObject=new Number(1333);numberObject.toPrecision(2);

"1.3e+3"

var numberObject=new Number(1333);numberObject.toPrecision(6);

"1333.00"

 

instanceof 可以判断对象的 原型