var a = "1", b = "2", c = "3", result;
// Step (1) Concatenate "1", "2", "3" into "123"
// - concatenation operator is just "+", as long
// as all the items are strings, this works
result = a + b + c; //123 string
// - If they were not strings you could do
result = a.toString() + b.toString() + c.toString(); // 123 string
// Step (2) Convert "123" into 123 (base 10)
result = parseInt(result, 10); // 123 number
// Step (3) Add 123 + 100 = 223
result = result + 100; // 223 number
// Step (4) Convert 223 into "223"
end_result = result.toString(); // 223 string
// If you concatenate a number with a
// blank string, you get a string
end_result = result + ""; //223 string