CODEWITHSUNDEEP
javascript
savinger
savinger

Reputation: 6714

Javascript parseInt() with leading zeros

Javascript's parseInt function does not seem to completely work.

parseInt("01") returns 1
parseInt("02") returns 2
parseInt("03") returns 3
parseInt("04") returns 4
parseInt("05") returns 5
parseInt("06") returns 6
parseInt("07") returns 7
parseInt("08") returns 0
parseInt("09") returns 0

You can't explain that. Give it a try. (jsFiddle)

Edit Since this question was asked and answered, the "feature" of defaulting to octal radix has been deprecated. [1] [2]

Upvotes: 135

Views: 80463

Answers (7)

Wayne
Wayne

Reputation: 60414

Calls to parseInt should always specify a base in the second argument:

parseInt("08", 10);

Earlier versions of JavaScript treat strings starting with 0 as octal (when no base is specified) and neither 08 nor 09 are valid octal numbers.

From the Mozilla documentation:

If radix is undefined or 0, JavaScript assumes the following:

  • If the input string begins with "0x" or "0X", radix is 16 (hexadecimal).
  • If the input string begins with "0", radix is eight (octal). This feature is non-standard, and some implementations deliberately do not support it (instead using the radix 10). For this reason always specify a radix when using parseInt.
  • If the input string begins with any other value, the radix is 10 (decimal).

If the first character cannot be converted to a number, parseInt returns NaN.

And from the ECMAScript 3 standard:

When radix is 0 or undefined and the string's number begins with a 0 digit not followed by an x or X, then the implementation may, at its discretion, interpret the number either as being octal or as being decimal. Implementations are encouraged to interpret numbers in this case as being decimal.

The latest version of JavaScript (ECMAScript 5) abandons this behavior, but you should still specify the radix to satisfy older browsers.

Upvotes: 45

mythicalcoder
mythicalcoder

Reputation: 3291

The issue seems to have changed now in most browsers.

Firefox 51.0.1 (64-bit)

parseInt("09")   // 9

Chrome 55.0.2883.95 (64-bit)

parseInt("09")   // 9

Safari 10.0 (12602.1.50.0.10)

parseInt("09")   // 9

=====

Recommended Practice

Having said that, just to be on the safer side and to avoid issues, use the base/radix parameter as suggested in the accepted answer.

parseInt("09", 10)    // 9

Extra test

I just wanted to test this as well, if the argument is not a string. Chrome & Safari gives exact result. Firefox too returns proper result, but with a warning.

parseInt(09)     // 9. (Warning: SyntaxError: 09 is not a legal ECMA-262 octal constant)

Upvotes: 0

Muhammad Imran
Muhammad Imran

Reputation: 744

This issue is deprecated now. But you can still use radix in parseInt to convert number of other bases into base-10. E.g.,

var baseTwoNumber = parseInt('0010001', 2);

returns 17 (which is base-10 of 0010001).

Upvotes: 3

Endless
Endless

Reputation: 37806

Tip: As you now know when default to octal has been deprecated. Here is how you would fix it in legacy browsers

// ES-5 15.1.2.2
if (parseInt('08') !== 8 || parseInt('0x16') !== 22) {
    parseInt = (function (origParseInt) {
        var hexRegex = /^0[xX]/;
        return function parseIntES5(str, radix) {
            str = String(str).trim();
            if (!Number(radix)) {
                radix = hexRegex.test(str) ? 16 : 10;
            }
            return origParseInt(str, radix);
        };
    }(parseInt));
}

Upvotes: 0

Maffelu
Maffelu

Reputation: 2068

This doesn't seem to be completely valid in new browsers. Internet Explorer 9 and 10 will return 8 if you execute 'parseInt("08")' whereas Internet Explorer 8 and previous versions will return 0 (IE10 in quirks mode will also return 0).

The latest version of Chrome also returns 8 so they must have changed the interpretation recently.

Upvotes: 4

John Hartsock
John Hartsock

Reputation: 86872

There is a Radix parameter

parseInt(value, base)

Where base is the radix.

In this case you are evaluating base10 (decimal) numbers, therefore use

parseInt(value, 10);

Upvotes: 16

gen_Eric
gen_Eric

Reputation: 227230

This is because if a number starts with a '0', it's treated as base 8 (octal).

You can force the base by passing the base as the 2nd parameter.

parseInt("09", 10) // 9

According to the docs, the 2nd parameter is optional, but it's not always assumed to be 10, as you can see from your example.

Upvotes: 192

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