var id = "23188xtr"; var lastName = "Smith"; var res=str.toUpperCase(); var userName= id;
Instead of naming the variable you wanted to change, you had named the function you're using that is you were meant to say:
var userName = id.toUpperCase();
so that a Upper case version of id is assigned to username.
Right now saying str.toUpperCase(); makes the computer look for a variable named "str". You had to substitute the variable name. Hope this helps, mufesi wangu.