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curriculum/challenges/english/blocks/learn-recursion-by-building-a-decimal-to-binary-converter/64005eb6d2d06a15d9f7611f.md

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--description--

In an earlier project you learned about truthy and falsy values, which are values that evaluate to true or false. In JavaScript, some common falsy values you'll see are null, undefined, the number 0, and empty strings.

Rather than check if a value is equal to a falsy value, you can use the <dfn>logical NOT</dfn> operator (!) to check if the value itself is falsy. For example:

js
const num = 0;

console.log(num === 0); // true
console.log(!num); // true

Update the condition in your if statement to use the logical NOT operator to check if numberInput.value is falsy.

--hints--

You should use the logical NOT operator (!) to check if numberInput.value is falsy.

js
assert.match(String(checkUserInput), /if\s*\(\s*!\s*numberInput\s*\.\s*value\s*\)\s*\{|if\s*\(\s*!\s*numberInput\s*\[\s*('|"|`)value\1\s*\]\s*\)\s*\{/)

The body of your if statement within checkUserInput should be empty.

js
assert.match(String(checkUserInput), /if\s*\(\s*.+\s*\)\s*\{\s*\}/);

--seed--

--seed-contents--

html
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Decimal to Binary Converter</title>
    <link rel="stylesheet" href="styles.css" />
  </head>
  <body>
    <h1>
      Decimal to Binary 

      Converter
    </h1>
    <section class="input-container">
      <label for="number-input">Enter a decimal number:</label>
      <input
        value=""
        type="number"
        name="decimal number input"
        id="number-input"
        class="number-input"
      />
      <button class="convert-btn" id="convert-btn">Convert</button>
    </section>
    <section class="output-container">
      <output id="result" for="number-input"></output>
      <h2>Call stack</h2>
      <div id="animation-container"></div>
    </section>
    <script src="script.js"></script>
  </body>
</html>
css
*,
*::before,
*::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

:root {
  --light-grey: #f5f6f7;
  --dark-blue: #1b1b32;
  --orange: #f1be32;
}

body {
  display: flex;
  flex-direction: column;
  align-items: center;
  font-family: Menlo, Consolas, Monaco, Liberation Mono, Lucida Console,
    monospace;
  font-size: 1.125rem;
  color: var(--light-grey);
  background-color: var(--dark-blue);
  padding: 0 4px;
}

h1 {
  font-size: 2.125rem;
  text-align: center;
  margin: 20px 0;
}

h2 {
  font-size: 1.5rem;
  text-align: center;
  margin: 20px 0;
}

.input-container {
  display: flex;
  flex-direction: column;
  gap: 10px;
  justify-content: center;
  align-items: center;
  width: clamp(320px, 50vw, 460px);
  margin: 10px auto;
}

.input-container label {
  white-space: nowrap;
  word-spacing: -6px;
}

.convert-btn {
  font-size: inherit;
  font-family: inherit;
  background-color: var(--orange);
  width: 100%;
  height: 2rem;
  padding: 0 6px;
  border: none;
  border-radius: 2px;
  cursor: pointer;
}

.number-input {
  font-size: inherit;
  padding: 0.3rem;
  width: 100%;
}

.output-container {
  margin-inline: auto;
  width: clamp(320px, 50vw, 460px);
}

#result {
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 2rem;
  text-align: center;
  min-height: 80px;
  margin-block-start: 20px;
  padding: 15px;
  border: 2px solid var(--orange);
  border-radius: 2px;
}

#animation-container {
  display: flex;
  flex-direction: column-reverse;
  justify-content: end;
  gap: 1rem;
  margin-block-end: 1rem;
  min-height: 40vh;
  border: 2px dashed var(--orange);
  padding: 1rem;
}

.animation-frame {
  font-family: -apple-system, BlinkMacSystemFont, avenir next, avenir, segoe ui,
    helvetica neue, helvetica, Cantarell, Ubuntu, roboto, noto, arial,
    sans-serif;
  padding: 15px 10px;
  border: 5px solid var(--orange);
  font-size: 1.2rem;
  text-align: center;
}

@media screen and (min-width: 36em) {
  body {
    font-size: 1rem;
  }

  .input-container {
    flex-direction: row;
    width: unset;
  }

  .number-input {
    width: unset;
  }
}
js
const numberInput = document.getElementById("number-input");
const convertBtn = document.getElementById("convert-btn");
const result = document.getElementById("result");

const checkUserInput = () => {
  --fcc-editable-region--
  if (numberInput.value === "") {

  }
  --fcc-editable-region--

  console.log(numberInput.value);
};

convertBtn.addEventListener("click", checkUserInput);

numberInput.addEventListener("keydown", (e) => {
  if (e.key === "Enter") {
    checkUserInput();
  }
});