How to convert a hexadecimal string to Uint8Array and back in JavaScript?

Question

I want to convert a hexadecimal string like bada55 into a Uint8Array and back again.

Answer 1

Node.js

For JavaScript running on Node you can do this:

const hexString = 'bada55';

const hex = Uint8Array.from(Buffer.from(hexString, 'hex'));

const backToHexString = Buffer.from(hex).toString('hex');

(source: this answer by @Teneff, shared with permission)

Answer 2

Here's a solution in native JavaScript:

var string = 'bada55';
var bytes = new Uint8Array(Math.ceil(string.length / 2));
for (var i = 0; i < bytes.length; i++) bytes[i] = parseInt(string.substr(i * 2, 2), 16);
console.log(bytes);

var convertedBack = '';
for (var i = 0; i < bytes.length; i++) {
  if (bytes[i] < 16) convertedBack += '0';
  convertedBack += bytes[i].toString(16);
}
console.log(convertedBack);

Answer 3

Browser (mimic NodeJS behavior acurately)

I had a need to mimic the NodeJS Buffer.from(x, 'hex') behavior in the browser environment and This is what I came up with.

It's pretty fast when I ran it through some benchmarks.

const HEX_STRINGS = "0123456789abcdef";
const MAP_HEX = {
  0: 0, 1: 1, 2: 2, 3: 3, 4: 4, 5: 5, 6: 6,
  7: 7, 8: 8, 9: 9, a: 10, b: 11, c: 12, d: 13,
  e: 14, f: 15, A: 10, B: 11, C: 12, D: 13,
  E: 14, F: 15
};

// Fast Uint8Array to hex
function toHex(bytes) {
  return Array.from(bytes || [])
    .map((b) => HEX_STRINGS[b >> 4] + HEX_STRINGS[b & 15])
    .join("");
}

// Mimics Buffer.from(x, 'hex') logic
// Stops on first non-hex string and returns
// https://github.com/nodejs/node/blob/v14.18.1/src/string_bytes.cc#L246-L261
function fromHex(hexString) {
  const bytes = new Uint8Array(Math.floor((hexString || "").length / 2));
  let i;
  for (i = 0; i < bytes.length; i++) {
    const a = MAP_HEX[hexString[i * 2]];
    const b = MAP_HEX[hexString[i * 2 + 1]];
    if (a === undefined || b === undefined) {
      break;
    }
    bytes[i] = (a << 4) | b;
  }
  return i === bytes.length ? bytes : bytes.slice(0, i);
}

Answer 4

like i've mentioned in the comments. this is not an easy task for a beginner. This code should give you a start though.

the biggest problem here is, that the results are loading in via an iframe, so you need to get this first.

Take a look at this code, it will get the basic info of the profiles and will return them as json. if you need some more explantion on this, feel free to ask in the comments.

import re
from selenium import webdriver
from selenium.webdriver.common.by import By
from selenium.webdriver.support import expected_conditions as EC
from selenium.webdriver.support.wait import WebDriverWait


def get_profile_info(profile_url):
    # gets info of a profile page // Adjust here to get more info
    wd.get(profile_url)
    label_element = WebDriverWait(wd, 5).until(
        EC.presence_of_element_located((By.ID, "labelAddress"))
    )
    label = label_element.find_element_by_tag_name("h1").text

    street = label_element.find_element_by_css_selector(
        "span[itemprop='streetAddress']"
    ).text

    postal_code = label_element.find_element_by_css_selector(
        "span[itemprop='postalCode']"
    ).text

    city = label_element.find_element_by_css_selector(
        "span[itemprop='addressLocality']"
    ).text

    address_region = label_element.find_element_by_css_selector(
        "span[itemprop='addressRegion']"
    ).text

    country = label_element.find_element_by_css_selector(
        "span[itemprop='addressCountry']"
    ).text

    return {
        "label": label,
        "street": street,
        "postal_code": postal_code,
        "city": city,
        "address_region": address_region,
        "country": country,
    }


def get_profile_url(label_element):
    # get the url from a result element
    onlick = label_element.get_attribute("onclick")
    # some regex magic
    return re.search(r"(?<=open\(\')(.*?)(?=\')", onlick).group()


def load_more_results():
    # load more results if needed // use only on the search page!
    button_wrapper = wd.find_element_by_class_name("loadNextBtn")
    button_wrapper.find_element_by_tag_name("span").click()


#### Script starts here ####

# Set some Selenium Options
options = webdriver.ChromeOptions()
options.add_argument("--no-sandbox")
options.add_argument("--disable-dev-shm-usage")

# Webdriver
wd = webdriver.Chrome(options=options)
# Load URL
wd.get("https://www.techpilot.de/zulieferer-suchen?laserschneiden")


# lets first wait for the timeframe
iframe = WebDriverWait(wd, 5).until(
    EC.frame_to_be_available_and_switch_to_it("efficientSearchIframe")
)

# the result parent
result_pane = WebDriverWait(wd, 5).until(
    EC.presence_of_element_located((By.ID, "resultPane"))
)


result_elements = wd.find_elements_by_class_name("fancyCompLabel")

# lets first collect all the links visible
href_list = []
for element in result_elements:
    url = get_profile_url(element)
    href_list.append(url)

# lets collect all the data now
result = []
for href in href_list:
    result.append(get_profile_info(href))

wd.close

# lets see what we've got
print(result)