HELP, how to write string into array of char

Hi Expert,

I'm trying to write js to pass string value into the request module resolution field (which OOB is array of 1 char)

when I try the following 

vars.$L_file.resolution = "test";

I got the error of "cannot store a string into an object of type array at char 1"

Please advice how to push value into data type array of char

 

Thanks

Soong