Javascript parseInt gives very unexpected results

Question

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Workarounds for JavaScript parseInt octal bug

I'm parsing a string to check if it's a date, and by chance we now discovered that my method doesn't work for dates in august or september. This is what I do (the input isn't really hard-coded, obviously, but for brevity...):

var str = '2010-08-26 14:53';
var data = str.split(' ');  // ['2010-08-26', '14:53']
var date = data[0].split('-'); // ['2010', '08', '26]
var time = data[1].split(':'); // ['14', '53']

var yyyy = parseInt(date[0]); // 2010

// THIS IS WHERE STRANGE THINGS HAPPEN:
var MM = parseInt(date[1]); // 0 - not 08 or 8, as expected!
console.log(date[1]); // prints "08" (with quotes)
console.log(date[1].toString()); // prints 08 (no quotes)
console.log(parseInt(date[1].toString())); // prints 0 (!)

This problem arises for august and september, and for the 8th and 9th every month - that is, when either "08" or "09" is being parsed to integer, 0 is returned instead of 8 or 9. The code works for both lower (e.g. "07") and higher (e.g. "10") integers (at least within expected date ranges...)

What am I doing wrong?

Answer 1

Use

parseInt(date[1], 10)

to make sure the string is interpreted as base 10 (decimal).

Otherwise, it is interpreted as base 8 (octal) if it starts with "0", or as base 16 (hexadecimal) if it starts with "0x".

In fact, you should always include the base argument to avoid these kinds of bugs.

Answer 2

That's because numbers that start with 0 are treated as octal numbers and "08" is not an octal so 0 is returned.

Read this: http://mir.aculo.us/2010/05/12/adventures-in-javascript-number-parsing/

Answer 3

The parseInt() function has the second optional radix parameter. If the radix parameter is omitted, JavaScript assumes the following:

• If the string begins with "0x", the radix is 16 (hexadecimal)
• If the string begins with "0", the radix is 8 (octal). This feature is deprecated
• If the string begins with any other value, the radix is 10 (decimal)

So in your case it assumes the octal numbers. Change to var MM = parseInt(date[1], 10); and it will work

Answer 4

It sounds like your date is being parsed as hex - the leading zero is doing this.

Because the hex and decimal representations are the same for 0-7 it 'works', but 8 and 9 get incorrectly converted.

Use

parseInt(date[1], 10)

To specify the base explicitly.