获取n-m之间的随机数

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);
                //或者 Math.floor(Math.random()*( maxNum - minNum + 1 ) + minNum );
                break;
            default:
                return 0;
                break;
        }
    }