Question

I am trying to add numbers as strings using basic math. I first set the local storage to “0” then add “1” to it each time. I feel I am on the right path, but when I run this my result is not 0 + 1 = 1 rather I get “01” in my local storage. I want to be able to add 1 to the existing local storage each time so 0 + 1 I get 1. Next time around 1 + 1 I get 2, and 2 + 1 I get 3 and so on.

// sets "points" to 0 when user first loads page.
if (localStorage.getItem("points") === null){
localStorage.setItem("points", "0");
}

// get points
var totalPoints = localStorage.getItem("points");
// add 1 points to exisiting total
var addPoint = totalPoints +"1";
// set new total
localStorage.setItem("points", addPoint);

Answer 1

You can convert a string to a number in several ways (not an exhaustive list):

var n = s * 1; // s is the string
var n = s - 0;
var n = parseFloat(s);
var n = Number(s);
var n = ~~s; // force to 32-bit integer
var n = parseInt(s, 10); // also integer, precise up to 53 bits

Convert your strings to numbers when you fetch them from local storage, do the math, and then put the results back.

edit — the thing to keep in mind is that + is more “interesting” than the other arithmetic operators because it has meaning for string-valued operands. In fact, JavaScript tends to prefer string interpretation of the + operator, so if there’s a string on one side and a number on the other, the operation is string concatenation and not arithmetic addition.