What is the best method to convert floating point to an integer in JavaScript?

Question

There are several different methods for converting floating point numbers to Integers in JavaScript. My question is what method gives the best performance, is most compatible, or is considered the best practice?

Here are a few methods that I know of:

var a = 2.5; window.parseInt(a); // 2 Math.floor(a);      // 2 a | 0;              // 2 

I'm sure there are others out there. Suggestions?

Answer 1

According to this website:

parseInt is occasionally used as a means of turning a floating point number into an integer. It is very ill suited to that task because if its argument is of numeric type it will first be converted into a string and then parsed as a number...

For rounding numbers to integers one of Math.round, Math.ceil and Math.floor are preferable...

Answer 2

Apparently double bitwise-not is the fastest way to floor a number:

var x = 2.5; console.log(~~x); // 2 

Used to be an article here, getting a 404 now though: http://james.padolsey.com/javascript/double-bitwise-not/

Google has it cached: http://74.125.155.132/search?q=cache:wpZnhsbJGt0J:james.padolsey.com/javascript/double-bitwise-not/+double+bitwise+not&cd=1&hl=en&ct=clnk&gl=us

But the Wayback Machine saves the day! http://web.archive.org/web/20100422040551/http://james.padolsey.com/javascript/double-bitwise-not/