How do I convert a float number to a whole number in JavaScript?

Question

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.

Answer 1

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

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Examples

Positive

// value=x        //  x=5          5<x<5.5      5.5<=x<6    Math.floor(value) //  5            5            5 Math.ceil(value)  //  5            6            6 Math.round(value) //  5            5            6 Math.trunc(value) //  5            5            5 parseInt(value)   //  5            5            5 ~~value           //  5            5            5 value | 0         //  5            5            5 value >> 0        //  5            5            5 value >>> 0       //  5            5            5 value - value % 1 //  5            5            5 

Negative

// value=x        // x=-5         -5>x>=-5.5   -5.5>x>-6  Math.floor(value) // -5           -6           -6 Math.ceil(value)  // -5           -5           -5 Math.round(value) // -5           -5           -6 Math.trunc(value) // -5           -5           -5 parseInt(value)   // -5           -5           -5 value | 0         // -5           -5           -5 ~~value           // -5           -5           -5 value >> 0        // -5           -5           -5 value >>> 0       // 4294967291   4294967291   4294967291 value - value % 1 // -5           -5           -5 

Positive - Larger numbers

// x = Number.MAX_SAFE_INTEGER/10 // =900719925474099.1  // value=x            x=900719925474099    x=900719925474099.4  x=900719925474099.5             Math.floor(value) //  900719925474099      900719925474099      900719925474099 Math.ceil(value)  //  900719925474099      900719925474100      900719925474100 Math.round(value) //  900719925474099      900719925474099      900719925474100 Math.trunc(value) //  900719925474099      900719925474099      900719925474099 parseInt(value)   //  900719925474099      900719925474099      900719925474099 value | 0         //  858993459            858993459            858993459 ~~value           //  858993459            858993459            858993459 value >> 0        //  858993459            858993459            858993459 value >>> 0       //  858993459            858993459            858993459 value - value % 1 //  900719925474099      900719925474099      900719925474099 

Negative - Larger numbers

// x = Number.MAX_SAFE_INTEGER/10 * -1 // -900719925474099.1  // value = x      // x=-900719925474099   x=-900719925474099.5 x=-900719925474099.6  Math.floor(value) // -900719925474099     -900719925474100     -900719925474100 Math.ceil(value)  // -900719925474099     -900719925474099     -900719925474099 Math.round(value) // -900719925474099     -900719925474099     -900719925474100 Math.trunc(value) // -900719925474099     -900719925474099     -900719925474099 parseInt(value)   // -900719925474099     -900719925474099     -900719925474099 value | 0         // -858993459           -858993459           -858993459 ~~value           // -858993459           -858993459           -858993459 value >> 0        // -858993459           -858993459           -858993459 value >>> 0       //  3435973837           3435973837           3435973837 value - value % 1 // -900719925474099     -900719925474099     -900719925474099 

Answer 2

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 ^{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