JavaScript: Array is undefined

Question

I have a multi-line variable and want to select a random line:

$.get('namelist.txt', function(nameList) {
 name = nameList.split('\n');
 var i = random();
 alert(name[i]); // this is undefined
});

The random() function returns a random number:

function random() {
 return Math.floor(Math.random()*201);
}

The problem is that the alert says undefined. If I replace line 3 with var i = 5, it works. I tested i with typeof and they're numbers in both cases. Any ideas on how to fix this?

• Emmerman: Maybe name have less than 200 elements?
• Tim B James: Are there 200 items in the array?
• T.J. Crowder: You really want to put var in front of name in your function. Without it, unless you have name defined in the scope enclosing the code you've quoted, you're overwriting the window.name property (which is almost certainly not what you want). In general, be sure to declare your variables so as not to fall prey to The Horror of Implicit Globals.

Answer 1

You should generate a random number depending on the length of the array. 201 is probably exceeding the highest index of your array.

You could adjust your random function to accept a length instead:

function random(len) {
 return Math.floor(Math.random() * len);
}

And then use it like this:

var name = nameList.split('\n');
var i = random(name.length);
alert(name[i]);

Array documentation reference

• mplungjan: as in function random() { return Math.floor(Math.random()*nameList.length); }
• Emmerman: Only remove -1 from here :)
• Emmerman: @Kevin Nope. random() never returns 1 so it never return 10. And in your example you can get -1 as a result
• jbrookover: @Kevin: Math.random() generates numbers less than one (e.g. 0.04) and if 'len' is 10, Math.floor(0.4) == 0. If you subtract 1 from that, you'll have an invalid index.
• Kevin: Asked a question because I was doubting myself and my english: stackoverflow.com/questions/5580579/javascript-math-random

Answer 2

Thsi is because the name is an array

which may contains around let say 3 element in it

if the random function have value more than 3 it will give you an error as you have right now.

on suggestion

first change no element in the array and the number generated by the random function.

if (name.length< randomnumber)
{
 //do logic what you want 
}

Answer 3

Is it possible there are less than 201 lines of text in nameList.txt?

Answer 4

var i = Math.floor(Math.random()*name.length);

Answer 5

Did you try

var i = parseInt(random());

?

• T.J. Crowder: Math.floor doesn't return a string.