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Binary to Decimal App using Typescript. #beginner2advanced

This is the first project in the beginner’s category in the #beginner2advanced challenge.

The application requirement can be found here.

In this article, we will be creating a web app where users can input numbers up to the length of 8 binary digits (0s and 1s), in any sequence and displays the decimal equivalent of the input number.

NOTE: This project is created using HTML, CSS and Typescript.

The end result of the application will look like this:


Creating our HTML and CSS file

First, we create an index.html and a style.css file as below.

<!-- index.html -->
<!DOCTYPE html>
<html lang="en">
    <title>Bin Dec</title>
    <link rel="stylesheet" href="./style.css" />
      <div id="dec">Example</div>
      <input id="binary-input" type="text" />
      <div id="error"></div>
    <script src="main.js"></script>
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Then we will include this simple stylesheet to style our application.

/* style.css */
body {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;

#binary-input {
  border: 1px solid #000;
  border-radius: 10px;
  height: 35px;
  width: 200px;
  padding: 0 20px;

#binary-input:focus {
  outline: 2px solid black;

#error {
  text-align: center;
  margin-top: 10px;
  color: red;

#dec {
  text-align: center;
  margin-bottom: 10px;
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The Typescript Code

// main.ts
const binInput = <HTMLInputElement>document.getElementById("binary-input");
const errorElem = <HTMLDivElement>document.getElementById("error");
const decElem = <HTMLDivElement>document.getElementById("dec");

// function to convert from binary to decimal
const bin2dec = (number: string) => {
  return parseInt(number, 2);

let timeoutMan: NodeJS.Timeout;

// display an error if any and remove the display in 0.5 second
const displayError = (error: string) => {
  errorElem.textContent = error;
  if (timeoutMan) {
  timeoutMan = setTimeout(() => {
    errorElem.innerText = "";
  }, 1000 * 0.5);

const is0or1 = (key: string) => {
  return key === "0" || key === "1";

const validateError = (key: string) => {
  if (is0or1(key)) {
    return key;
  } else {
    displayError("input either 0 or 1");
    return "";

const displayDecimal = (number: string) => {
  decElem.innerText = `Decimal: ${bin2dec(number)}`;

// the state of input coming in our project
let inputText = "";

binInput.addEventListener("keydown", (event) => {
  if (event.key === "Backspace") {
    inputText = inputText
      .slice(0, inputText.length - 1)

    binInput.value = inputText;
  } else {
    if (binInput.value.length >= 8) {
      return displayError("cannot be above 8 digits");
    inputText += validateError(event.key);
    binInput.value = inputText;
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Thanks for reading. You can configure your Typescript to compile into any folder structure of your choice and include the generated JavaScript code in your index.html.

You can find how I did this in this repository.

If you enjoy reading this article, you can consider buying me a coffee.

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