Javascript eval ReferenceError: is not defined

Question

I need to dynamical create a variable off the value of a variable from an argument I am pulling in from a script. But I first want to check if it already exists so I don't overwrite it, if it is already set.

I am leveraging eval to expand the value of the variable and tag it onto a variable suffix but no matter what I use to check for the undefined I am getting a reference error on the check.

Below is the simple code snippet

chkUser = args[1];

if(typeof eval(chkUser+"lastseen")==="undefined") ;

I've also tried put the eval in parens and putting undefined in ' ' and pulled them completely and switching typeof to the JavaScript standard undefined as such

if( eval(chkUser+"lastseen")=== undefined) ;

but I always get ReferenceError: robertlastseen is not defined or what ever chkUser expands out to.

Answer 1

Its just a guess, but it seems like the Variable is just not defined before you eval it.

try this Fiddle.

It works fine for me.

Try to hard-code the variable before you eval it like this:

chkUser = args[1];
var robertlastseen = 'Hardcode';
console.log(eval(chkUser+"lastseen"));

Then you should be able to debug your code.

if you just want to test if this Variable is declared try this:

if(eval('typeof ' + chkUser + 'lastseen') === "undefined"){
    //Variable undefined
}