Question

I am trying to make a function which are supposed to check if a certain date is in the correct format.
Do to this, the function takes in a variable, and breaks it down to three subvariables, year, month, and day. Later on I want to check each of these substrings against in a few if-statements.

When i run this with my GFs number which is 880413 then year=88, month=4, day=13
However, when I run this function with my own number which is 820922, then the function sets year to 82, month to 0?! and day=22.

How is this possibe? when month is 04, it cuts it off and shows only 4, but when month is 09 it cuts it off to 0.

Heres relevant code:

function isValidDate(date) 
{
    var valid = true;

    var year = parseInt(date.substring(0, 2));
    var month = parseInt(date.substring(2, 4)); // error here!
    var day = parseInt(date.substring(4, 6));
    alert(year+"--"+month+"--"+day+"--")
}

Heres output when running number 820922 (forget about the last 4 digits, they are for swedish social security number and do no need to be considered in this example)

And heres output with number 880413 (again forget about the last 4 digits)

Answer 1

Always specify a radix when using parseInt()

The reason for this is if you don’t specify it, it doesn’t default to base 10, instead it guesses based on the first digit/character. IE if it starts with a ‘0’ then it is intepreted as octal

function isValidDate(date) 
{
    var valid = true;

    var year = parseInt(date.substring(0, 2), 10);
    var month = parseInt(date.substring(2, 4), 10);
    var day = parseInt(date.substring(4, 6), 10);
    alert(year+"--"+month+"--"+day+"--")
}

Or use Number() ie

var month = Number(date.substring(2, 4));