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Build a Roman Numeral Converter

curriculum/challenges/english/blocks/build-a-roman-numeral-converter-project/657bdc8ba322aae1eac38390.md

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--description--

Roman numerals are based on seven symbols and can be written using various combinations to represent Arabic numerals. For example:

Roman numeralsArabic numerals
M1000
CM900
D500
CD400
C100
XC90
L50
XL40
X10
IX9
V5
IV4
I1

Objective: Build an app that is functionally similar to <a href="https://roman-numeral-converter.freecodecamp.rocks" target="_blank" rel="noopener noreferrer nofollow">https://roman-numeral-converter.freecodecamp.rocks</a>.

User Stories:

  1. You should have an input element with an id of "number".
  2. You should have a button element with an id of "convert-btn".
  3. You should have a div, span or p element with an id of output.
  4. When you click on the #convert-btn element without entering a value into the #number element, the #output element should contain the text "Please enter a valid number".
  5. When the #number element contains the number -1 and the #convert-btn element is clicked, the #output element should contain the text "Please enter a number greater than or equal to 1".
  6. When the #number element contains the number 4000 or greater and the #convert-btn element is clicked, the #output element should contain the text "Please enter a number less than or equal to 3999".
  7. When the #number element contains the number 9 and the #convert-btn element is clicked, the #output element should contain the text "IX".
  8. When the #number element contains the number 16 and the #convert-btn element is clicked, the #output element should contain the text "XVI".
  9. When the #number element contains the number 649 and the #convert-btn element is clicked, the #output element should contain the text "DCXLIX".
  10. When the #number element contains the number 1023 and the #convert-btn element is clicked, the #output element should contain the text "MXXIII".
  11. When the #number element contains the number 3999 and the #convert-btn element is clicked, the #output element should contain the text "MMMCMXCIX".

Fulfill the user stories and pass all the tests below to complete this project. Give it your own personal style. Happy Coding!

--hints--

You should have an input element with an id of "number".

js
const el = document.getElementById('number');
assert.strictEqual(el?.nodeName?.toLowerCase(), 'input');

You should have a button element with an id of "convert-btn".

js
const el = document.getElementById('convert-btn');
assert.strictEqual(el?.nodeName?.toLowerCase(), 'button');

You should have a div, span, or p element with an id of "output".

js
const el = document.getElementById('output');
assert(['div', 'span', 'p'].includes(el?.nodeName?.toLowerCase()));

When you click on the #convert-btn element without entering a value into the #number element, the #output element should contain the text "Please enter a valid number".

js
const numberInputEl = document.getElementById('number');
const convertBtnEl = document.getElementById('convert-btn');
const outputEl = document.getElementById('output');

numberInputEl.value = '';
convertBtnEl.click();
assert.strictEqual(outputEl.innerText.trim().replace(/[.,?!]+$/g, '').toLowerCase(), 'please enter a valid number');

When the #number element contains the number -1 and the #convert-btn element is clicked, the #output element should contain the text "Please enter a number greater than or equal to 1".

js
const numberInputEl = document.getElementById('number');
const convertBtnEl = document.getElementById('convert-btn');
const outputEl = document.getElementById('output');

numberInputEl.value = '-1';
numberInputEl.dispatchEvent(new Event('change'));
convertBtnEl.click();
assert.strictEqual(outputEl.innerText.trim().replace(/[.,?!]+$/g, '').toLowerCase(), 'please enter a number greater than or equal to 1');

When the #number element contains the number 4000 or greater and the #convert-btn element is clicked, the #output element should contain the text "Please enter a number less than or equal to 3999".

js
const numberInputEl = document.getElementById('number');
const convertBtnEl = document.getElementById('convert-btn');
const outputEl = document.getElementById('output');

numberInputEl.value = '4000';
numberInputEl.dispatchEvent(new Event('change'));
convertBtnEl.click();
assert.strictEqual(outputEl.innerText.trim().replace(/[.,?!]+$/g, '').toLowerCase(), 'please enter a number less than or equal to 3999');

When the #number element contains the number 9 and the #convert-btn element is clicked, the #output element should contain the text "IX".

js
const numberInputEl = document.getElementById('number');
const convertBtnEl = document.getElementById('convert-btn');
const outputEl = document.getElementById('output');

numberInputEl.value = '9';
numberInputEl.dispatchEvent(new Event('change'));
convertBtnEl.click();
assert.strictEqual(outputEl.innerText.trim(), 'IX');

When the #number element contains the number 16 and the #convert-btn element is clicked, the #output element should contain the text "XVI".

js
const numberInputEl = document.getElementById('number');
const convertBtnEl = document.getElementById('convert-btn');
const outputEl = document.getElementById('output');

numberInputEl.value = '16';
numberInputEl.dispatchEvent(new Event('change'));
convertBtnEl.click();
assert.strictEqual(outputEl.innerText.trim(), 'XVI');

When the #number element contains the number 649 and the #convert-btn element is clicked, the #output element should contain the text "DCXLIX".

js
const numberInputEl = document.getElementById('number');
const convertBtnEl = document.getElementById('convert-btn');
const outputEl = document.getElementById('output');

numberInputEl.value = '649';
numberInputEl.dispatchEvent(new Event('change'));
convertBtnEl.click();
assert.strictEqual(outputEl.innerText.trim(), 'DCXLIX');

When the #number element contains the number 1023 and the #convert-btn element is clicked, the #output element should contain the text "MXXIII".

js
const numberInputEl = document.getElementById('number');
const convertBtnEl = document.getElementById('convert-btn');
const outputEl = document.getElementById('output');

numberInputEl.value = '1023';
numberInputEl.dispatchEvent(new Event('change'));
convertBtnEl.click();
assert.strictEqual(outputEl.innerText.trim(), 'MXXIII');

When the #number element contains the number 3999 and the #convert-btn element is clicked, the #output element should contain the text "MMMCMXCIX".

js
const numberInputEl = document.getElementById('number');
const convertBtnEl = document.getElementById('convert-btn');
const outputEl = document.getElementById('output');

numberInputEl.value = '3999';
numberInputEl.dispatchEvent(new Event('change'));
convertBtnEl.click();
assert.strictEqual(outputEl.innerText.trim(), 'MMMCMXCIX');

When the #number element contains a random negative number and the #convert-btn element is clicked, the #output element should contain the text "Please enter a number greater than or equal to 1".

js
const numberInputEl = document.getElementById('number');
const convertBtnEl = document.getElementById('convert-btn');
const outputEl = document.getElementById('output');

const randomNegativeNumber = Math.floor(Math.random() * -4000) - 2; 

numberInputEl.value = randomNegativeNumber;
numberInputEl.dispatchEvent(new Event('change'));
convertBtnEl.click();
assert.strictEqual(outputEl.innerText.trim().replace(/[.,?!]+$/g, '').toLowerCase(), 'please enter a number greater than or equal to 1');

When the #number element contains a number greater than 4000 and the #convert-btn element is clicked, the #output element should contain the text "Please enter a number less than or equal to 3999".

js
const numberInputEl = document.getElementById('number');
const convertBtnEl = document.getElementById('convert-btn');
const outputEl = document.getElementById('output');

const randomBigNumber = Math.floor(Math.random() * (1000000)) + 4000; 

numberInputEl.value =  randomBigNumber;
numberInputEl.dispatchEvent(new Event('change'));
convertBtnEl.click();
assert.strictEqual(outputEl.innerText.trim().replace(/[.,?!]+$/g, '').toLowerCase(), 'please enter a number less than or equal to 3999');

--seed--

--seed-contents--

html
css
js

--solutions--

html
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />
    <link
      href="https://fonts.googleapis.com/css2?family=Castoro+Titling&display=swap"
      rel="stylesheet"
    />
    <link rel="stylesheet" type="text/css" href="styles.css" />
    <link
      rel="icon"
      type="image/png"
      href="https://cdn.freecodecamp.org/universal/favicons/favicon.ico"
    />
    <title>Roman Numeral Converter</title>
  </head>
  <body>
    <main>
      
      <h1>Roman Numeral Converter</h1>
      <form id="form" class="form">
        <fieldset>
          <label for="number">Enter a Number:</label>

          <input type="number" id="number" required />
          <button type="button" id="convert-btn">Convert</button>
        </fieldset>
      </form>
      <div id="output" class="output hidden"></div>
    </main>
    <script src="script.js"></script>
  </body>
</html>
css
:root {
  --gray-00: #ffffff;
  --gray-05: #f5f6f7;
  --gray-15: #d0d0d5;
  --gray-75: #3b3b4f;
  --gray-85: #1b1b32;
  --gray-90: #0a0a23;
  --blue-50: #198eee;
  --error: #a94442;
  --danger-color: #850000;
  --danger-background: #ffadad;
}

*,
::before,
::after {
  padding: 0;
  margin: 0;
  box-sizing: border-box;
}

body {
  min-height: 100vh;
  padding: 50px 20px;
  font-family: 'Lato', Helvetica, Arial, sans-serif;
  font-size: 18px;
  background-color: var(--gray-85);
  color: var(--gray-05);
}

main {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
}

.freecodecamp-logo {
  height: 30px;
  margin-bottom: 20px;
}

h1 {
  text-align: center;
  margin: 20px auto;
  max-width: 350px;
  font-family: 'Castoro Titling', cursive;
}

form {
  color: var(--gray-05);
  margin: auto 25px;
  padding: 15px auto;
  border: 3px solid var(--gray-05);
  text-align: center;
  width: 90%;
  max-width: 500px;
  background-color: var(--gray-75);
}

fieldset {
  border: 0 none;
  height: 100%;
  padding: 25px;
  margin: 10px 20px;
}

label {
  display: inline-block;
  font-size: 1.5rem;
  margin-bottom: 10px;
  font-weight: bold;
}

input:focus-visible,
button:focus-visible {
  outline: 3px solid var(--blue-50);
}

input {
  display: block;
  font-size: 2.5rem;
  width: 100%;
  height: 60px;
  padding: 6px 12px;
  margin: 10px 0;
  line-height: 1.4;
  color: white;
  background-color: var(--gray-90);
  border: 1px solid var(--gray-05);
}

button {
  cursor: pointer;
  margin-top: 15px;
  text-decoration: none;
  background-image: linear-gradient(#fecc4c, #ffac33);
  border: 3px solid #feac32;
  padding: 10px 16px;
  font-size: 23px;
  width: 100%;
}

.output {
  color: white;
  background-color: var(--gray-75);
  border: 3px solid var(--gray-05);
  font-size: 2.5rem;
  width: 90%;
  max-width: 500px;
  min-height: 55px;
  margin-top: 25px;
  padding: 15px;
  overflow-wrap: break-word;
  text-align: center;
}

.alert {
  font-size: 2rem;
  background-color: var(--danger-background);
  border: 3px solid var(--danger-color);
  color: var(--danger-color);
}

.hidden {
  display: none;
}
js
const form = document.getElementById("form");
const convertButton = document.getElementById("convert-btn");
const output = document.getElementById("output");

const convertToRoman = (num) => {
  const ref = [
    ["M", 1000],
    ["CM", 900],
    ["D", 500],
    ["CD", 400],
    ["C", 100],
    ["XC", 90],
    ["L", 50],
    ["XL", 40],
    ["X", 10],
    ["IX", 9],
    ["V", 5],
    ["IV", 4],
    ["I", 1],
  ];
  const res = [];

  ref.forEach(function (arr) {
    while (num >= arr[1]) {
      res.push(arr[0]);
      num -= arr[1];
    }
  });

  return res.join("");
};

const isValid = (str, int) => {
  let errText = "";

  if (!str || str.match(/[e.]/g)) {
    errText = "Please enter a valid number.";
  } else if (int < 1) {
    errText = "Please enter a number greater than or equal to 1.";
  } else if (int > 3999) {
    errText = "Please enter a number less than or equal to 3999.";
  } else {
    // No errors detected
    return true;
  }

  // Handle error text and output styling
  output.innerText = errText;
  output.classList.add("alert");

  return false;
};

const clearOutput = () => {
  output.innerText = "";
  output.classList.remove("alert");
};

form.addEventListener("submit", (e) => {
  e.preventDefault();
  updateUI();
});

convertButton.addEventListener("click", () => {
  updateUI();
});

const updateUI = () => {
  const numStr = document.getElementById("number").value;
  const int = parseInt(numStr, 10);

  output.classList.remove("hidden");

  clearOutput();

  if (isValid(numStr, int)) {
    output.innerText = convertToRoman(int);
  }
};