How can I remove the decimal part from JavaScript number?

Question

I have the results of a division and I wish to discard the decimal portion of the resultant number.

How can I do this?

Answer 1

let x = 9 / 2;
console.log(x); // 4.5

x = ~~x;
console.log(x); // 4

x = -3.7
console.log(~~x) // -3
console.log(x | 0) // -3
console.log(x << 0) // -3

Answer 2

You can also use bitwise operators to truncate the decimal.

e.g.

let x = 9 / 2;
console.log(x); // 4.5

x = ~~x;
console.log(x); // 4

x = -3.7
console.log(~~x) // -3
console.log(x | 0) // -3
console.log(x << 0) // -3

Bitwise operations are considerably more efficient than the Math functions. The double not bitwise operator also seems to slightly outperform the x | 0 and x << 0 bitwise operations by a negligible amount.

// 952 milliseconds
for (var i = 0; i < 1000000; i++) {
    (i * 0.5) | 0;
}

// 1150 milliseconds
for (var i = 0; i < 1000000; i++) {
    (i * 0.5) << 0;
}

// 1284 milliseconds
for (var i = 0; i < 1000000; i++) {
    Math.trunc(i * 0.5);
}

// 939 milliseconds
for (var i = 0; i < 1000000; i++) {
    ~~(i * 0.5);
}

Also worth noting is that the bitwise not operator takes precedence over arithmetic operations, so you may need to surround calculations with parentheses to have the intended result:

const x = -3.7

console.log(~~x * 2) // -6
console.log(x * 2 | 0) // -7
console.log(x * 2 << 0) // -7

console.log(~~(x * 2)) // -7
console.log(x * 2 | 0) // -7
console.log(x * 2 << 0) // -7

More info about the double bitwise not operator can be found at Double bitwise NOT (~~)

You also should ensure that your integer will not need more than 32-bits to represent:

const a = 0x100000000 + 0.1; // 4294967296.1
console.log(Math.trunc(a)); // 4294967296
console.log(~~a); // 0

Answer 3

Here is the compressive in detailed explanation with the help of previous posts:

1. Math.trunc() : It is used to remove those digits which are followed by dot. It converts implicitly. But, not supported in IE.

Example:

Math.trunc(10.5) // 10
Math.trunc(-10.5) // -10    

Other Alternative way: Use of bitwise not operator:

Example:

x= 5.5
~~x // 5

2. Math.floor() : It is used to give the minimum integer value posiible. It is supported in all browsers.

Example:

Math.floor(10.5) // 10
Math.floor(-10.5) // -11

3. Math.ceil() : It is used to give the highest integer value possible. It is supported in all browsers.

Example:

Math.ceil(10.5) // 11
Math.ceil(-10.5) // -10

4. Math.round() : It is rounded to the nearest integer. It is supported in all browsers.

Example:

Math.round(10.5) // 11
Math.round(-10.5)// -10
Math.round(10.49) // 10
Math.round(-10.51) // -11

Answer 4

You can also show a certain number of digit after decimal point (here 2 digits) using toFixed, which will return a string representation:

var num = (15.46974).toFixed(2)
console.log(num) // 15.47
console.log(typeof num) // string

Answer 5

In this examples I use Number.toFixed and Math.trunc methods:

const num = 1.234

Number(num.toFixed(0)); // Returns 1
Number(num.toFixed(2)); // Returns 1.23

Math.trunc(num); // Returns 1

The toFixed() method formats a number using fixed-point notation.
The Math.trunc() static method returns the integer part of a number by removing any fractional digits.

Answer 6

You can use .toFixed(0) to remove complete decimal part or provide the number in arguments upto which you want decimal to be truncated.

Note: toFixed will convert the number to string.

Answer 7

If you don't care about rouding, just convert the number to a string, then remove everything after the period including the period. This works whether there is a decimal or not.

const sEpoch = ((+new Date()) / 1000).toString();
const formattedEpoch = sEpoch.split('.')[0];

Answer 8

This is for those who want to prevent users to enter decimal numbers

<input id="myInput" onkeyup="doSomething()" type="number" />

<script>
    function doSomething() {

        var intNum = $('#myInput').val();

        if (!Number.isInteger(intNum)) {
            intNum = Math.round(intNum);
        }

        console.log(intNum);
    }
</script>

Answer 9

For an ES6 implementation, use something like the following:

const millisToMinutesAndSeconds = (millis) => {
  const minutes = Math.floor(millis / 60000);
  const seconds = ((millis % 60000) / 1000).toFixed(0);
  return `${minutes}:${seconds < 10 ? '0' : ''}${seconds}`;
}

Answer 10

You could use...

• Math.trunc() (truncate fractional part, also see below)
• Math.floor() (round down)
• Math.ceil() (round up)
• Math.round() (round to nearest integer)

...dependent on how you wanted to remove the decimal.

Math.trunc() isn't supported on all platforms yet (namely IE), but you could easily use a polyfill in the meantime.

Another method of truncating the fractional portion with excellent platform support is by using a bitwise operator (.e.g |0). The side-effect of using a bitwise operator on a number is it will treat its operand as a signed 32bit integer, therefore removing the fractional component. Keep in mind this will also mangle numbers larger than 32 bits.

---

You may also be talking about the inaccuracy of decimal rounding with floating point arithmetic.

Required Reading - What Every Computer Scientist Should Know About Floating-Point Arithmetic.

Answer 11

With ES2015, Math.trunc() is available.

Math.trunc(2.3)                       // 2
Math.trunc(-2.3)                      // -2
Math.trunc(22222222222222222222222.3) // 2.2222222222222223e+22
Math.trunc("2.3")                     // 2
Math.trunc("two")                     // NaN
Math.trunc(NaN)                       // NaN

It's not supported in IE11 or below, but does work in Edge and every other modern browser.

Answer 12

toFixed will behave like round.

For a floor like behavior use %:

var num = 3.834234;
var floored_num = num - (num % 1); // floored_num will be 3

Answer 13

Use Math.round() function.

Math.round(65.98) // will return 66 
Math.round(65.28) // will return 65

Answer 14

You could also do

parseInt(a/b)

Answer 15

Use Math.round().

(Alex's answer is better; I made an assumption :)