Javascript (+) sign concatenates instead of giving sum of variables

Use this instead:

var divID = "question-" + (i+1)

It's a fairly common problem and doesn't just happen in JavaScript. The idea is that + can represent both concatenation and addition.

Since the + operator will be handled left-to-right the decisions in your code look like this:

"question-" + i: since "question-" is a string, we'll do concatenation, resulting in "question-1"
"question-1" + 1: since "queston-1" is a string, we'll do concatenation, resulting in "question-11".

With "question-" + (i+1) it's different:

since the (i+1) is in parenthesis, its value must be calculated before the first + can be applied:
- i is numeric, 1 is numeric, so we'll do addition, resulting in 2
"question-" + 2: since "question-" is a string, we'll do concatenation, resulting in "question-2".

Use only:

divID = "question-" + parseInt(i) + 1;

When "n" comes from html input field or is declared as string, you need to use explicit conversion.

var n = "1"; //type is string
var frstCol = 5;
lstCol = frstCol + parseInt(n);

If "n" is integer, don't need conversion.

n = 1; //type is int
var frstCol = 5, lstCol = frstCol + n;

You may also use this

divID = "question-" + (i*1+1);

to be sure that i is converted to integer.

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