任意数求和

function sum() {
  let num = 0;
  for (let i = 0; i < arguments.length; i++) {
    //注意：typeof(NaN) => 'number',但是 (NaN === NaN) => false
    if (typeof (arguments[i]) === 'number' && parseFloat(arguments[i]) === parseFloat(arguments[i])) {
      num += arguments[i]
    }
  }
  return num
}
console.log(sum(1, 2.5, 3.8, '2px', 54, true, '', function () {}, {}, '2', NaN, -1  )); //61.3