How do I convert a float number to a whole number in JavaScript?
I'd like to convert a float to a whole number in JavaScript. Actually, I'd like to know how to do BOTH of the standard conversions: by truncating and by rounding. And efficiently, not via converting to a string and parsing.
var intvalue = Math.floor( floatvalue );
var intvalue = Math.ceil( floatvalue );
var intvalue = Math.round( floatvalue );
// `Math.trunc` was added in ECMAScript 6
var intvalue = Math.trunc( floatvalue );
Math object reference
Examples
Positivevalue = 5.5
Math.floor(value) // 5
Math.ceil(value) // 6
Math.round(value) // 6
Math.trunc(value) // 5
parseInt(value) // 5
~~value // 5
value | 0 // 5
value >> 0 // 5
value >>> 0 // 5
value - value % 1 // 5
value = -5.5
Math.floor(value) // -6
Math.ceil(value) // -5
Math.round(value) // -5
Math.trunc(value) // -5
parseInt(value) // -5
value | 0 // -5
~~value // -5
value >> 0 // -5
value >>> 0 // 4294967291
value - value % 1 // -5
value = Number.MAX_SAFE_INTEGER/10 // 900719925474099.1
Math.floor(value) // 900719925474099
Math.ceil(value) // 900719925474100
Math.round(value) // 900719925474099
Math.trunc(value) // 900719925474099
parseInt(value) // 900719925474099
value | 0 // 858993459
~~value // 858993459
value >> 0 // 858993459
value >>> 0 // 858993459
value - value % 1 // 900719925474099
value = Number.MAX_SAFE_INTEGER/10 * -1 // -900719925474099.1
Math.floor(value) // -900719925474100
Math.ceil(value) // -900719925474099
Math.round(value) // -900719925474099
Math.trunc(value) // -900719925474099
parseInt(value) // -900719925474099
value | 0 // -858993459
~~value // -858993459
value >> 0 // -858993459
value >>> 0 // 3435973837
value - value % 1 // -900719925474099
Bitwise OR operator
A bitwise or operator can be used to truncate floating point figures and it works for positives as well as negatives:
function float2int (value) {
return value | 0;
}
Results
float2int(3.1) == 3
float2int(-3.1) == -3
float2int(3.9) == 3
float2int(-3.9) == -3
Performance comparison?
I've created a JSPerf test that compares performance between:
Math.floor(val) val | 0 val | 0 bitwise OR ~~val bitwise NOT parseInt(val) that only works with positive numbers. In this case you're safe to use bitwise operations well as Math.floor function.
But if you need your code to work with positives as well as negatives , then a bitwise operation is the fastest (OR being the preferred one). This other JSPerf test compares the same where it's pretty obvious that because of the additional sign checking Math is now the slowest of the four.
Note
As stated in comments, BITWISE operators operate on signed 32bit integers, therefore large numbers will be converted, example:
1234567890 | 0 => 1234567890
12345678901 | 0 => -539222987
Note: You cannot use Math.floor() as a replacement for truncate, because Math.floor(-3.1) = -4 and not -3 !!
A correct replacement for truncate would be:
function truncate(value)
{
if (value < 0) {
return Math.ceil(value);
}
return Math.floor(value);
}