Convert Uint8Array into hex string equivalent in Node.js

Question

I am using Node.js v4.5. Suppose I have this Uint8Array variable.

var uint8 = new Uint8Array(4);
uint8[0] = 0x1f;
uint8[1] = 0x2f;
uint8[2] = 0x3f;
uint8[3] = 0x4f;

This array can be of any length but let's assume the length is 4.

I would like to have a function that that converts uint8 into the hex string equivalent.

var hex_string = convertUint8_to_hexStr(uint8);
// hex_string becomes "1f2f3f4f"

Uint8Array.prototype.toHex() arriving soon, and here is the polyfill: github.com/zloirock/core-js#uint8array-to--from-base64-and-hex — Yves M.
– Yves M., Commented Jan 28 at 7:41

robertklep · Accepted Answer · 2016-08-30 10:45:35Z

82

You can use Buffer.from() and subsequently use toString('hex'):

let hex = Buffer.from(uint8).toString('hex');

answered Aug 30, 2016 at 10:45

robertklep

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2 Comments

Filip Seman Over a year ago

This is a good answer for the Node.js use case, but it is not compatible with Deno or the browser.

robertklep Over a year ago

@FilipSeman good thing the question was tagged with node.js then :D

Tomasz Jakub Rup · Accepted Answer · 2020-02-09 20:45:55Z

15

Another solution:

Base function to convert int8 to hex:

// padd with leading 0 if <16
function i2hex(i) {
  return ('0' + i.toString(16)).slice(-2);
}

reduce:

uint8.reduce(function(memo, i) {return memo + i2hex(i)}, '');

Or map and join:

Array.from(uint8).map(i2hex).join('');

edited Feb 9, 2020 at 20:45

answered Aug 30, 2016 at 10:48

Tomasz Jakub Rup

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3 Comments

tintin Over a year ago

This does not padd correctly when the decimal value is <16. Here's a fixed version uint8.reduce(function(memo, i) { return memo + ("0"+i.toString(16)).slice(-2); }, '');

Motla Over a year ago

Second method works only for an Array but not Uint8Array, as the map function tries to write a string to the array (for Uint8Array it is casted to a number and evaluates to zero when there is a letter in the hex number). Workaround is to use Array.from(uint8) instead of uint8.

Joe Hildebrand Over a year ago

Slight modernization: uint8.reduce((t, x) => t + x.toString(16).padStart(2, '0'), '')

MoonSung Zhang · Accepted Answer · 2022-02-20 20:03:48Z

7

Buffer.from has multiple overrides.

If it is called with your uint8 directly, it unnecessarily copies its content because it selects Buffer.from( <Buffer|Uint8Array> ) version.

You should call Buffer.from( arrayBuffer[, byteOffset[, length]] ) version which does not copy and just creates a view of the buffer.

let hex = Buffer.from(uint8.buffer,uint8.byteOffset,uint8.byteLength).toString('hex');

edited Feb 20, 2022 at 20:03

answered Feb 16, 2022 at 12:55

MoonSung Zhang

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1 Comment

geon Over a year ago

Relevant documentation here: nodejs.org/api/…

MonstraG · Accepted Answer · 2025-04-29 19:18:51Z

7

Buffer is Node.js specific.

This is a version that works everywhere:

const uint8 = new Uint8Array(4);
uint8[0] = 0x1f;
uint8[1] = 0x2f;
uint8[2] = 0x3f;
uint8[3] = 0x4f;

function convertUint8_to_hexStr(uint8) {
  return Array.from(uint8)
    .map((i) => i.toString(16).padStart(2, '0'))
    .join('');
}

convertUint8_to_hexStr(uint8);

edited Apr 29 at 19:18

MonstraG

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answered Jan 27, 2023 at 15:12

Uriel

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