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

Posted by: admin February 21, 2020 Leave a comment

Questions:

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.

How to&Answers:
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

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:

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

Answer:

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);
}

Answer:

A double bitwise not operator can be used to truncate floats. The other operations you mentioned are available through Math.floor, Math.ceil, and Math.round.

> ~~2.5
2
> ~~(-1.4)
-1

More details courtesy of James Padolsey.

Answer:

For truncate:

var intvalue = Math.floor(value);

For round:

var intvalue = Math.round(value);

Answer:

You can use the parseInt method for no rounding. Be careful with user input due to the 0x (hex) and 0 (octal) prefix options.

var intValue = parseInt(floatValue, 10);

Answer:

Bit shift by 0 which is equivalent to division by 1

// >> or >>>
2.0 >> 0; // 2
2.0 >>> 0; // 2

Answer:

In your case, when you want a string in the end (in order to insert commas), you can also just use the Number.toFixed() function, however, this will perform rounding.

Answer:

There are many suggestions here. The bitwise OR seems to be the simplest by far. Here is another short solution which works with negative numbers as well using the modulo operator. It is probably easier to understand than the bitwise OR:

intval = floatval - floatval%1;

This method also works with high value numbers where neither ‘|0’ nor ‘~~’ nor ‘>>0’ work correctly:

> n=4294967295;
> n|0
-1
> ~~n
-1
> n>>0
-1
> n-n%1
4294967295

Answer:

One more possible way — use XOR operation:

console.log(12.3 ^ 0); // 12
console.log("12.3" ^ 0); // 12
console.log(1.2 + 1.3 ^ 0); // 2
console.log(1.2 + 1.3 * 2 ^ 0); // 3
console.log(-1.2 ^ 0); // -1
console.log(-1.2 + 1 ^ 0); // 0
console.log(-1.2 - 1.3 ^ 0); // -2

Priority of bitwise operations is less then priority of math operations, it’s useful. Try on https://jsfiddle.net/au51uj3r/

Answer:

To truncate:

// Math.trunc() is part of the ES6 spec
Math.trunc( 1.5 );  // returns 1
Math.trunc( -1.5 ); // returns -1
// Math.floor( -1.5 ) would return -2, which is probably not what you wanted

To round:

Math.round( 1.5 );  // 2
Math.round( 1.49 ); // 1
Math.round( -1.6 ); // -2
Math.round( -1.3 ); // -1

Answer:

If look into native Math object in JavaScript, you get the whole bunch of functions to work on numbers and values, etc…

Basically what you want to do is quite simple and native in JavaScript…

Imagine you have the number below:

const myValue = 56.4534931;

and now if you want to round it down to the nearest number, just simply do:

const rounded = Math.floor(myValue);

and you get:

56

If you want to round it up to the nearest number, just do:

const roundedUp = Math.ceil(myValue);

and you get:

57

Also Math.round just round it to higher or lower number depends on which one is closer to the flot number.

Also you can use of ~~ behind the float number, that will convert a float to a whole number.

You can use it like ~~myValue

Answer:

I just want to point out that monetarily you want to round, and not trunc. Being off by a penny is much less likely, since 4.999452 * 100 rounded will give you 5, a more representative answer.

And on top of that, don’t forget about banker’s rounding, which is a way to counter the slightly positive bias that straight rounding gives — your financial application may require it.

Gaussian/banker's rounding in JavaScript

Answer:

If you are using angularjs then simple solution as follows In HTML Template Binding

{{val | number:0}}

it will convert val into integer

go through with this link docs.angularjs.org/api/ng/filter/number