Ways to round down numbers in JavaScript without using the Math library

Question

Ways to round down numbers in JavaScript without using the Math library

Looking for a way to limit numbers to two decimal places, similar to currency. Previously used the following method:

Number(parseFloat(Math.trunc(amount_to_truncate * 100) / 100));

Now seeking an alternative without relying on the Math library but still avoiding rounding the decimals. Any suggestions?

javascript angularjs

Answer 1

Answer №1

One way to truncate numbers in JavaScript is by using the toFixed method.

Number(amount_to_truncate.toFixed(2))

If you are confident that the input will always be 21474836.47 or lower (32-bit), you can do:

To ensure the result has exactly two decimal places as a string:

((amount_to_truncate * 100|0)/100).toFixed(2)

Otherwise:

((amount_to_truncate * 100|0)/100)

Alternatively, check out Nina Schols's answer for more insights.

console.log((((15.555 * 100)|0)/100)) // This will not round: 15.55
console.log((((15 * 100)|0)/100).toFixed(2)) // This will also not round: 15.55

Answer 2

One way to truncate numbers in JavaScript is by using the toFixed method.

Number(amount_to_truncate.toFixed(2))

If you are confident that the input will always be 21474836.47 or lower (32-bit), you can do:

To ensure the result has exactly two decimal places as a string:

((amount_to_truncate * 100|0)/100).toFixed(2)

Otherwise:

((amount_to_truncate * 100|0)/100)

Alternatively, check out Nina Schols's answer for more insights.

console.log((((15.555 * 100)|0)/100)) // This will not round: 15.55
console.log((((15 * 100)|0)/100).toFixed(2)) // This will also not round: 15.55

Answer 3

Answer №2

Keep it straightforward

function truncateNumber(number, decimalPlaces) {
  const decimals = decimalPlaces ? decimalPlaces : 2;
  const numString = number.toString();
  const position = numString.indexOf('.') != -1 ? numString.indexOf('.') + decimals + 1 : numString.length;
  return parseFloat(number.toString().substring(0, position));
};

console.log(truncateNumber(3.14159265359));
console.log(truncateNumber(11.1111111));
console.log(truncateNumber(3));
console.log(truncateNumber(11));
console.log(truncateNumber(3.1));
console.log(truncateNumber(11.1));
console.log(truncateNumber(3.14));
console.log(truncateNumber(11.11));
console.log(truncateNumber(3.141));
console.log(truncateNumber(11.111));

Answer 4

Keep it straightforward

function truncateNumber(number, decimalPlaces) {
  const decimals = decimalPlaces ? decimalPlaces : 2;
  const numString = number.toString();
  const position = numString.indexOf('.') != -1 ? numString.indexOf('.') + decimals + 1 : numString.length;
  return parseFloat(number.toString().substring(0, position));
};

console.log(truncateNumber(3.14159265359));
console.log(truncateNumber(11.1111111));
console.log(truncateNumber(3));
console.log(truncateNumber(11));
console.log(truncateNumber(3.1));
console.log(truncateNumber(11.1));
console.log(truncateNumber(3.14));
console.log(truncateNumber(11.11));
console.log(truncateNumber(3.141));
console.log(truncateNumber(11.111));

Answer 5

Answer №3

One issue I notice with the toFixed function is that it rounds the precision, which goes against what the original poster (OP) wants. It seems like using the `truncate` method would be more suitable in this case, as it is similar to using floor for positive numbers and ceil for negative ones, rather than round or toFixed. The MDN page for Math.trunc provides a polyfill replacement function that aligns with OP's expectations.


Math.trunc = Math.trunc || function(x) {
  return x - x % 1;
}

Simply implementing this alternative function would solve the problem without requiring any other changes to the code.

Answer 6

One issue I notice with the toFixed function is that it rounds the precision, which goes against what the original poster (OP) wants. It seems like using the `truncate` method would be more suitable in this case, as it is similar to using floor for positive numbers and ceil for negative ones, rather than round or toFixed. The MDN page for Math.trunc provides a polyfill replacement function that aligns with OP's expectations.


Math.trunc = Math.trunc || function(x) {
  return x - x % 1;
}

Simply implementing this alternative function would solve the problem without requiring any other changes to the code.

Answer 7

Answer №4

If you want a non-rounded number, consider using the parseInt function in JavaScript.

console.log(parseInt(15.555 * 100, 10) / 100); // Result: 15.55 (no rounding)
console.log((15.555 * 100 | 0) / 100);         // Result: 15.55 (no rounding, 32 bit only)
console.log((15.555).toFixed(2));              // Result: 15.56 (rounding)

Answer 8

If you want a non-rounded number, consider using the parseInt function in JavaScript.

console.log(parseInt(15.555 * 100, 10) / 100); // Result: 15.55 (no rounding)
console.log((15.555 * 100 | 0) / 100);         // Result: 15.55 (no rounding, 32 bit only)
console.log((15.555).toFixed(2));              // Result: 15.56 (rounding)

Answer 9

Answer №5

Consider utilizing the toPrecision method:

num.toPrecision(3)

Answer 10

Consider utilizing the toPrecision method:

num.toPrecision(3)

Answer 11

Answer №6

It appears that truncating also involves rounding, so your request for numbers to have only two decimals without rounding them seems a bit complicated and may lead to a lengthy discussion.

In the context of dealing with money, the issue lies not with the Math object itself but rather in how it is being utilized. I recommend familiarizing yourself with the Floating-point cheat sheet for JavaScript to avoid potential pitfalls such as encountering incorrect results in basic calculations like 1.40 - 1.00.

To address your query, consider using a reliable library for handling arbitrary-precision decimals such as bignumber.js or decimals.js (just to name a few).

UPDATE:

If you require a quick code snippet, here's an approach I implemented previously:

function round2(d) { return Number(((d+'e'+2)|0)+'e-'+2); }

Answer 12

It appears that truncating also involves rounding, so your request for numbers to have only two decimals without rounding them seems a bit complicated and may lead to a lengthy discussion.

In the context of dealing with money, the issue lies not with the Math object itself but rather in how it is being utilized. I recommend familiarizing yourself with the Floating-point cheat sheet for JavaScript to avoid potential pitfalls such as encountering incorrect results in basic calculations like 1.40 - 1.00.

To address your query, consider using a reliable library for handling arbitrary-precision decimals such as bignumber.js or decimals.js (just to name a few).

UPDATE:

If you require a quick code snippet, here's an approach I implemented previously:

function round2(d) { return Number(((d+'e'+2)|0)+'e-'+2); }

Answer 13

Answer №7

To easily truncate a number in JavaScript, you can use parseInt followed by division and parseFloat.

var num = 123.4567;
num = parseInt(num * 100);
num = parseFloat(num / 100);
alert(num);

Check out this JSFiddle demo

Alternatively, to handle the quirks of JavaScript math, you can utilize .toFixed with an extra digit for multiplication and division:

var num = 123.4567;
num = (num * 1000).toFixed();
num = parseInt(num / 10);
num = parseFloat(num / 100);
alert(num);

Updated version: JSFiddle link

Answer 14

To easily truncate a number in JavaScript, you can use parseInt followed by division and parseFloat.

var num = 123.4567;
num = parseInt(num * 100);
num = parseFloat(num / 100);
alert(num);

Check out this JSFiddle demo

Alternatively, to handle the quirks of JavaScript math, you can utilize .toFixed with an extra digit for multiplication and division:

var num = 123.4567;
num = (num * 1000).toFixed();
num = parseInt(num / 10);
num = parseFloat(num / 100);
alert(num);

Updated version: JSFiddle link

Answer 15

Answer №8

Wow, I can't believe how simple this turned out to be:

const truncateNumber = (number, precision) => {
  let decimalIndex = number.toString().indexOf(".");
  let truncatedStr;

  // when there is no decimal point
  if (decimalIndex === -1) {
    truncatedStr = number.toString();
  }
  // when precision is set to 0
  else if (precision === 0) {
    truncatedStr = number.toString().substring(0, decimalIndex);
  }
  // for all other cases
  else {
    truncatedStr = number.toString().substring(0, decimalIndex + 1 + precision);
  }
  return parseFloat(truncatedStr);
};

let result = truncateNumber(99.12, 1);

console.log("Result:", result);

Answer 16

Wow, I can't believe how simple this turned out to be:

const truncateNumber = (number, precision) => {
  let decimalIndex = number.toString().indexOf(".");
  let truncatedStr;

  // when there is no decimal point
  if (decimalIndex === -1) {
    truncatedStr = number.toString();
  }
  // when precision is set to 0
  else if (precision === 0) {
    truncatedStr = number.toString().substring(0, decimalIndex);
  }
  // for all other cases
  else {
    truncatedStr = number.toString().substring(0, decimalIndex + 1 + precision);
  }
  return parseFloat(truncatedStr);
};

let result = truncateNumber(99.12, 1);

console.log("Result:", result);

Answer 17

Answer №9

Give this a shot

function roundDown(value){
    return (!!value && typeof value == "number")? value - value%1 : 0;
}
console.log(roundDown(1.4));
console.log(roundDown(111.9));
console.log(roundDown(0.4));
console.log(roundDown("1.4"));

Answer 18

Give this a shot

function roundDown(value){
    return (!!value && typeof value == "number")? value - value%1 : 0;
}
console.log(roundDown(1.4));
console.log(roundDown(111.9));
console.log(roundDown(0.4));
console.log(roundDown("1.4"));

Ways to round down numbers in JavaScript without using the Math library

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

Answer №6

Answer №7

Answer №8

Answer №9

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