獲取0-9的隨機數：randomNum（0，9）

//生成從minNum到maxNum的隨機數
function randomNum(minNum,maxNum){ 
  switch(arguments.length){ 
      case 1: 
          return parseInt(Math.random()*minNum+1,10); 
      break; 
      case 2: 
          return parseInt(Math.random()*(maxNum-minNum+1)+minNum,10); 
      break; 
          default: 
              return 0; 
          break; 
  } 
}