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?

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. — T.J. Crowder
– T.J. Crowder, Commented Apr 7, 2011 at 11:46

Kevin · Accepted Answer · 2011-04-07 11:44:07Z

4

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

edited Apr 7, 2011 at 11:44

answered Apr 7, 2011 at 11:36

Kevin

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8 Comments

mplungjan Over a year ago

as in function random() { return Math.floor(Math.random()*nameList.length); }

Emmerman Over a year ago

Only remove -1 from here :)

Emmerman Over a year ago

@Kevin Nope. random() never returns 1 so it never return 10. And in your example you can get -1 as a result

jbrookover Over a year ago

@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 Over a year ago

Asked a question because I was doubting myself and my english: stackoverflow.com/questions/5580579/javascript-math-random

|

Pranay Rana · Accepted Answer · 2011-04-07 11:37:59Z

1

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 
}

answered Apr 7, 2011 at 11:37

Pranay Rana

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Comments

Luke · Accepted Answer · 2011-04-07 11:40:20Z

0

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

answered Apr 7, 2011 at 11:40

Luke

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Comments

j0k · Accepted Answer · 2012-08-13 21:10:15Z

0

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

edited Aug 13, 2012 at 21:10

j0k

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answered Apr 7, 2011 at 11:38

Emmerman

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Comments

Rob_IGS · Accepted Answer · 2011-04-07 11:40:04Z

-1

Did you try

var i = parseInt(random());

?

answered Apr 7, 2011 at 11:40

Rob_IGS

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1 Comment

T.J. Crowder Over a year ago

Math.floor doesn't return a string.

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