Did you know that JavaScript's parseInt function to convert strings to integers has an optional second argument to explicitly define a radix? It specifies the base of the number you're going to parse. New JavaScript developers often assume that not specifying a base means it will use the most common one: base 10. This is not always true! Most JavaScript runtimes will attempt to guess the radix based on the start of the value. If the number begins with a 0, it will parse as octal (radix of 8). If the number starts with 0x, it will parse as hexadecimal (radix of 16).
That's why it's very important that our code always specify a radix.
Try it out: parseInt("09"); or parseInt("010");