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If you need to handle things like bit fields or 32-bit colors, then you need to deal with signed numbers. The JavaScript function toString(16) will return a negative hexadecimal number which is usually not what you want. This function does some crazy addition to make it a positive number.

function decimalToHexString(number)
{
  if (number < 0)
  {
    number = 0xFFFFFFFF + number + 1;
  }

  return number.toString(16).toUpperCase();
}

console.log(decimalToHexString(27));
console.log(decimalToHexString(48.6));

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developer.mozilla.org › en-US › docs › Web › JavaScript › Reference › Global_Objects › Uint8Array › toHex

Uint8Array.prototype.toHex() - JavaScript - MDN Web Docs

The toHex() method of Uint8Array instances returns a hex-encoded string based on the data in this Uint8Array object.

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reddit.com › r/javascript › javascript can't output non-string hex values, can it?

r/javascript on Reddit: JavaScript can't output non-string hex values, can it?

November 3, 2015 -

I'm aware that JS recognizes hex values, e.g. 0xFF0000, but am I correct in thinking that it can't actually output them as anything other than strings or decimal integers? In other words, you could hard code x to be equal to 0xFF0000, but you couldn't set it to that value dynamically, right?

Obviously you could set it to the decimal equivalent, or to a string containing the hex value (i.e. "0xFF0000"), and you can always use toString and parseInt with a base of 16 to translate back and forth, but you can't actually output hex-encoded integers directly. Am I right?

Top answer

1 of 2

To convert an integer to a hexadecimal value in JavaScript, you can use the Number.toString() method and specify a radix of 16 (hexadecimal) as the second argument. For example, to convert the integer 7654321 to a hexadecimal value, you could use the following code:

const intValue = 7654321;
const hexValue = intValue.toString(16);
console.log(hexValue);  // Output: "b1bcd1"

In Web3.js, you can use the web3.utils.toHex() method to convert an integer to a hexadecimal value. This method takes the integer value as the first argument and an optional second argument that specifies the number of characters in the resulting hexadecimal value. For example, to convert the integer 7654321 to a hexadecimal value with 8 characters, you could use the following code:

const intValue = 7654321;
const hexValue = web3.utils.toHex(intValue, 8);
console.log(hexValue);  // Output: "00000b1bcd1"

You can then use the hexValue variable in your automation script as needed.

2 of 2

Found the answer in another thread:

ethereumjs-util has relevant methods: setLengthLeft and bufferToHex:

const util = require('ethereumjs-util');    
util.bufferToHex(util.setLengthLeft(123, 2))
'0x007b'
util.bufferToHex(util.setLengthLeft(3, 32))
'0x0000000000000000000000000000000000000000000000000000000000000003'

MDN Web Docs

developer.mozilla.org › en-US › docs › Web › JavaScript › Reference › Global_Objects › Uint8Array › fromHex

Uint8Array.fromHex() - JavaScript - MDN Web Docs

July 10, 2025 - Thrown if the input string contains characters outside the hex alphabet, or its length is odd.

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August 22, 2023 - The hex() function in p5.js is used to convert a number into its hexadecimal notation.

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JavaScript HEX encoding · GitHub

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