What is the best method to convert 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

parseInt() is probably the best one. a | 0 doesn't do what you really want (it just assigns 0 if a is an undefined or null value, which means an empty object or array passes the test), and Math.floor works by some type trickery (it basically calls parseInt() in the background).

Answer 2

You can use Number(a).toFixed(0);

Or even just a.toFixed(0);

Edit:

That's rounding to 0 places, slightly different than truncating, and as someone else suggested, toFixed returns a string, not a raw integer. Useful for display purposes.

var num = 2.7;  // typeof num is "Number"
num.toFixed(0) == "3"

Answer 3

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 4

var i = parseInt(n, 10);

If you don't specify a radix values like '010' will be treated as octal (and so the result will be 8 not 10).

Answer 5

To everyone suggesting parseInt: read the original post again, carefully. a is a numeric variable, not a string.

Answer 6

The question appears to be asking specifically about converting from a float to an int. My understanding is that the way to do this is to use toFixed. So...

var myFloat = 2.5;
var myInt = myFloat.toFixed(0);

Does anyone know if Math.floor() is more or less performant than Number.toFixed()?

Answer 7

The answer has already been given but just to be clear.

Use the Math library for this. round, ceil or floor functions.

parseInt is for converting a string to an int which is not what is needed here

toFixed is for converting a float to a string also not what is needed here

Since the Math functions will not be doing any conversions to or from a string it will be faster than any of the other choices which are wrong anyway.

Answer 8

you could also do it this way:

var string = '1';
var integer = a * 1;

Answer 9

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