DEV Community: Jan Prazak

Get all separate digits of a number (TypeScript)

Jan Prazak — Wed, 06 Jul 2022 12:53:09 +0000

Do you need to "extract" each digit of a given number? Then this little TypeScript program is probably exactly what you're looking for. I have inserted some important comments about the "safe" input range, so make sure you are aware of it before using it in critical segments. There are many different solutions, this one avoids converting the number to a String internally, so it's a pure mathematical algorithm. (Note: I have updated the code to work correctly if given number is 0.)

/**
 * @param num A number in the int32 range [-2147483648 .. 2147483647]
 * @returns A number[] containing each digit of `num`.
 * If negative `num` given, resulting array will contain negatives numbers.
 */
function separateDigits(num: number): number[] {
  let arr: number[] = [];
  let lastDigit: number;

  num = toInt32(num);

  do {
    lastDigit = num % 10;
    arr.push(lastDigit);
    // Updating num to num/10 cuts off the last digit:
    num = toInt32(num / 10);
  }
  while (num !== 0);

  return arr.reverse();
}

/**
* Fast bitwise operation, truncates floating point number resulting in int32.
* The >> bitwise operator is used, an overflow occurs if number too large.
* A *safe* integer division in JavaScript would be Math.floor(x/y);
* @param f A (JavaScript) number between [-2147483648.999 .. 2147483647.999]
* @returns Input 'f' truncated to Int32.
*/
function toInt32(f: number): number {
  // Note that type "number" in JS is always "float" internally.
  return f >> 0;
}

console.log(separateDigits(3142520));

// Output:
// [3, 4, 1, 2, 5, 2, 0]

randomUUID in TypeScript

Jan Prazak — Wed, 06 Jul 2022 12:49:55 +0000

How to add missing support

As of today (May 2022) TypeScript type definition files lack Crypto API's randomUUID method.

I came up with this short solution which doesn't require modifying the typedef files. It is a simple workaround which exports the randomUUID method as generateUUID, and also checks browser support (returns an empty string if not supported in your browser). Maybe it will be of some use to others until TS gets updated.

More about randomUUID on MDN here. Overview of browser support here

export {generateUUID};

interface CryptoNew extends Crypto {
  randomUUID?() : string;
}

/**
 * Returns an empty string if Crypto API or randomUUID is not supported by browser.
 */
function generateUUID() : string {
  let cryptoRef: CryptoNew;
  let r: string | undefined = "";

  if (typeof self.crypto !== "undefined") {
    cryptoRef = self.crypto;
    r = cryptoRef.randomUUID?.();
  }

  return r ? r : "";
}

OMDb-search (JS code demo)

Jan Prazak — Tue, 30 Jun 2020 12:52:10 +0000

JavaScript demo: search for movies in The OMDb (The Open Movie Database).

So finally I "finished" one of my learning projects in a way it can actually be useful to someone.

It uses some important features of ES6, namely JS modules and asynchronous XHR. I intentionally avoided using the new Fetch API to show how the old good XHR can be transformed into async mode, it shows nicely how promises work in modern JS. It also uses the WebStorage API (localStorage - for storing the API key to browser) and the Web Animations API for the loader animation.

GitHub project page: https://github.com/Amarok24/OMDb-search

Screenshot:

Prime numbers - Sieve of Eratosthenes

Jan Prazak — Tue, 07 Jan 2020 12:05:32 +0000

Sieve of Eratosthenes in pure (vanilla) JavaScript.

detect BigEndian LittleEndian (JS)

Jan Prazak — Tue, 03 Dec 2019 11:14:59 +0000

Detect endianness of current CPU/MPU. Big Endian or Little Endian. Detection in vanilla JavaScript.

Ramda library - compose, map, sum

Jan Prazak — Wed, 21 Aug 2019 16:14:17 +0000

A test of a few useful functions, using the popular Ramda library for functional programming. I really like this library! Just visit www.ramdajs.com

Copying objects with Object.assign()

Jan Prazak — Wed, 21 Aug 2019 09:51:51 +0000

The weird part of Object.assign finally cracked :-) This is a short code snippet which explains how Object.assign() works. There is some console output but everything important is already written in JS code comments.

User-Agent (browser) detection

Jan Prazak — Tue, 13 Aug 2019 10:14:35 +0000

Here is a short snippet which I use for browser environment sniffing throught JavaScript, code is inspired by Vue.js sourcecode from 7/2019.

var inBrowser = typeof window !== "undefined";
var browser_UA = inBrowser && window.navigator.userAgent.toLowerCase();
var browser_isIE = browser_UA && /msie|trident/.test(browser_UA);
var browser_isIE11 = browser_isIE && browser_UA.indexOf('11.0') > 0;
var browser_isEdge = browser_UA && browser_UA.indexOf('edge/') > 0;
var browser_isAndroid = browser_UA && browser_UA.indexOf('android') > 0;
var browser_isIOS = browser_UA && /iphone|ipad|ipod|ios/.test(browser_UA);
var browser_isChrome = browser_UA && /chrome\/\d+/.test(browser_UA) && !browser_isEdge;
var browser_isGoogleChrome = browser_isChrome && !!window.googleapis;
var browser_isChromeDerivate = browser_isChrome && !browser_isGoogleChrome;
var browser_isFirefox = browser_UA && !!browser_UA.indexOf("firefox/");

//ANOTHER:
var browser_FFversion = browser_isFirefox && browser_UA.match(/firefox\/(\d+)/)[1];
// FF version then stored in array[1]

Hello world

Jan Prazak — Wed, 24 Jul 2019 09:21:07 +0000

First post? OK, this, what else :-D

console.log("Hello world");