That means when we reach 3, the start of a new string using double quotes, it's an unexpected string. You probably want: ... At 1, we start the string.

Understanding the Context

2 is just a " within the string, it doesn't end it. 3 ends it, then we append checkval, then we start a new string (4) with a " in it (5) followed by a ] and then the end of the string (6).