JavaScript ParseInt Radix

Jul 02 2013


Today I came across an error while I was linting my Intelligent RGB / HEX Converter Plugin code about requiring a radix value for parseInt(). After a quick look up on Google I could see that excluding this parameter could lead to some rather nasty bugs in your code. The radix parameter is meant to specify the number system to use when parsing the value passed into parseInt(). So if we pass in a value of 16 then the number system used would be hexadecimal and a value of 8 would be octal.

The reason why this value is important is because in older web browsers like ie7 and ie8 any value with a leading zero automatically gets parsed as an octal value. So if you happened to pass in a string of 012 this would actually get parsed as the octal value 10.

For example if we put this in to ie7 or ie8:

console.log(parseInt('012'));      // 10
console.log(parseInt('012', 8));   // 10
console.log(parseInt(012, 8));     // 8
console.log(parseInt('012', 10));  // 12

If we’re writing an application that might by chance have leading zeros in it, we would really have a nasty bug leaving out that radix value. Most browsers will now treat all values as decimal using 10 as the default number system and ignoring the leading zeros. The one exception being a leading value of 0x for hexadecimal values. So for instance the two following values will both get parsed using base 16.

console.log(parseInt('0x12'));     // 18
console.log(parseInt('0x12', 16)); // 18

However ie7 and ie8 are still in use and avoiding this bug is quite simple by just putting a 10 into the parseInt() parameter. I never use to be a big fan of linting but I find I use it all the time now to catch simple bugs like this. A great tool you can use for linting is called Grunt.js which you can setup to automate tasks like linting, testing and minifying your JavaScript and CSS code. I have previously written a guide on Setting up Grunt.js that you can read on setting it up which can be a lifesaver for avoiding little bugs like the missing radix value.


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