Eval reference error

Question

In javascript i am building up a string like this...

var txt = "{authenticationToken: 1, authenticated: 2, authenticationTokenExpiry: 3,sessionTimeoutMinutes: 4,userName: " + userName + "}";

This is later put through and eval statement like this...

var obj = eval('(' + txt + ')');

When this happenings I get a reference error saying the the value of the username variable is undefined.

Does anyone know the reason for this? Is it something simple that I am missing?

Is there a reason you're not using [`JSON.parse`](https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/JSON/parse) instead of `eval`? — James Allardice, Jul 06 '12 at 15:30
`eval ('(' + txt + ')')`? But anyway, where is `userName` defined? — raina77ow, Jul 06 '12 at 15:30
This is to run on an old Blackberry phone where json.parse doesn't work. — Ben Cameron, Jul 06 '12 at 15:32
Are you sure your variable isn't called `username` rather than `userName`? — Graham, Jul 06 '12 at 15:32
Sorry I missed the + signs in the post but they are there in the real code. — Ben Cameron, Jul 06 '12 at 15:32
@BenCameron - Consider using a [polyfill](https://github.com/douglascrockford/JSON-js/) so you can still use `JSON.parse` reliably. — James Allardice, Jul 06 '12 at 15:33
Any reason you are creating the JSON and not just an object? — iambriansreed, Jul 06 '12 at 15:33
I'd make sure to validate that JSON first, otherwise you have a sizeable security hole using eval(). — Matt Gibson, Jul 06 '12 at 15:36

score 1 · Accepted Answer · answered Jul 06 '12 at 15:53

Your missing quotes around the username variable:

var txt = "{authenticationToken: 1, authenticated: 2, authenticationTokenExpiry: 3,sessionTimeoutMinutes: 4,userName: '" + userName + "'}";

I assume you want to store the string value of the username in your userName variable. Since it wasn't quoted it was treating the value of username as a variable. So for example if username was "testValue123" it would of been userName: testValue123 instead of userName: 'testValue123'

Robert · Answer 2 · 2012-07-06T16:00:15.960

Instead of eval(), I would suggest using the $.parseJSON() method if jQuery is available:

jQuery:

$(function(){
    var userName = 'me';

    var txt = '{"authenticationToken": 1, "authenticated": 2, "authenticationTokenExpiry": 3, "sessionTimeoutMinutes": 4, "userName": "' + userName + '"}';

    var obj = $.parseJSON(txt);
});

NOTE: The string had to be modified to satisfy the requirement of a well-formed JSON string

Demo: http://jsfiddle.net/WTC7k/

However, the reason that you're encountering the error that the value of userName is undefined is that you have to enclose the string in quotes to allow eval() to work properly:

var userName = 'me';

var txt = "{authenticationToken: 1, authenticated: 2, authenticationTokenExpiry: 3,sessionTimeoutMinutes: 4,userName: '" + userName + "'}"; 

var obj = eval('(' + txt + ')');

Demo: http://jsfiddle.net/9rtgK/

Yes that would be ideal but sadly this code is for a Blackberry application on an older model. JSON.parse isn't available. — Ben Cameron, Jul 09 '12 at 07:27

Eval reference error

2 Answers2