目的:获取某一范围的随机数
function selectFrom(lowerValue,upperValue){
var choices=upperValue-lowerValue+1;
return Math.floor(Math.random()*choices+lowerValue);
}
var num=selectForm(2,10);
alert(num); //返回介于2—10的一个随机数
利用这个函数,可以方便地从数组中随机取出一项,例如
var colors=["red","green","blue","yellow","black","purple","brown"];
var color=colors[selectForm(0,colors.length-1)];
alert(color);//数组中随机一项