random()方法

 1 function selectFrom(lowerValue, upperValue) {
 2             var choices = upperValue - lowerValue + 1;
 3             return Math.floor(Math.random() * choices + lowerValue);
 4         }
 5 
 6         var num = selectFrom(2, 10);
 7         console.log(num);
 8         
 9         var colors = ["red", "green", "blue", "yellow", "black", "purple", "brown"];
10         var color = colors[selectFrom(0, colors.length - 1)];
11         console.log(color);