来自数组的随机生成字母的问题

Question

Sometimes the randomly-generated letter equals to 'undefined'

Anyone know why?

Code:

<script type="text/javascript"> 
var myArray= ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'];

randomnumber=Math.floor(Math.random()*27);
alert(myArray[randomnumber]);

Answer 1

Well, it could have something to do with your Math.floor(Math.random()*27) using the number 27 when there are 26 letters in the English alphabet.

math random returns 0-.999... 
math random * 27 returns 0-26.999...
floor math random * 27 returns 0 - 26 
an array with every english letter has 26 items 
which means it has items indexed from 0-25

so you get a blank in each box 1/27 of all loads. However, once "#next" has been seeded it will always stay a "letter" because you're replacing it with

$("#next").text(good[randomnumber]);

When randomnumber=27 good[randomnumber]=undefined and $("#next").text(undefined) does nothing so the contents of "#next" remain unchanged. Still broken, less obvious. Just change 27 to 26 and you're done.