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Unit Price Compare

Compare grocery unit prices to find the genuinely cheaper option.

food
30 downloads

By Lucas

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name: Unit Price Compare description: "Compare grocery unit prices to find the genuinely cheaper option." category: food connections: [] version: 1

What it does

Unit Price Compare cuts through confusing shelf prices. Enter up to three grocery products with name, price, and pack size (g, kg, ml, L, oz, or lb) and it instantly computes the price per 100 g / 100 ml for each, normalizing everything to a common unit. It highlights the cheapest per-unit option with a badge and a summary of the percentage difference. Ideal for deciding between a big bag and a small box in the grocery aisle; everything recalculates live as you type.

Setup

  • Open app.html directly in any modern browser (works via file://, no server needed).
  • No persistence and no setup; two fictional sample rows ("Sample Oats A" / "Sample Oats B") show the math on first load — rename and edit them freely.
  • Enter each product's price, size, and unit; use "+ Add a product" for a third item (max 3).
  • The cheapest per-unit option is highlighted automatically; the summary shows how much less per unit it is versus the priciest.

Source

app.html — the complete app (single self-contained file: HTML, CSS, and JavaScript, no external dependencies):

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Unit Price Compare</title>
<style>
  :root {
    --bg: #0f1b2d;
    --card: #17263d;
    --ink: #eef3fa;
    --muted: #93a3bb;
    --accent: #34d399;
    --accent-dim: #1f6f54;
    --gold: #fbbf24;
    --line: #29405e;
  }
  * { box-sizing: border-box; }
  body {
    margin: 0;
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
    background: var(--bg);
    color: var(--ink);
    line-height: 1.5;
  }
  .wrap {
    max-width: 560px;
    margin: 0 auto;
    padding: 20px 16px 48px;
  }
  header h1 { font-size: 1.8rem; margin: 0 0 4px; }
  header h1 .up { color: var(--accent); }
  .sub { color: var(--muted); margin: 0 0 20px; }
  .card {
    background: var(--card);
    border: 1px solid var(--line);
    border-radius: 12px;
    padding: 16px;
    margin-bottom: 14px;
  }
  .card.cheapest {
    border: 2px solid var(--accent);
    box-shadow: 0 0 14px rgba(52, 211, 153, .25);
    position: relative;
  }
  .badge {
    display: inline-block;
    background: var(--accent);
    color: #06281c;
    font-weight: bold;
    font-size: .75rem;
    border-radius: 999px;
    padding: 2px 10px;
    margin-bottom: 8px;
  }
  .row { display: flex; gap: 10px; }
  .row > * { flex: 1; }
  label { display: block; margin: 10px 0 4px; color: var(--muted); font-size: .85rem; }
  input, select {
    width: 100%;
    padding: 10px 12px;
    border: 1px solid var(--line);
    border-radius: 8px;
    font-size: 1rem;
    background: #0e1930;
    color: var(--ink);
  }
  input:focus, select:focus { outline: 2px solid var(--accent); border-color: var(--accent); }
  .name-label { margin-top: 0; }
  .result {
    margin-top: 12px;
    padding-top: 12px;
    border-top: 1px dashed var(--line);
    font-size: 1.05rem;
  }
  .result .ppu { font-weight: bold; color: var(--accent); font-size: 1.15rem; }
  .card.cheapest .result .ppu { color: var(--gold); }
  .empty-result { color: var(--muted); font-style: italic; }
  .summary {
    text-align: center;
    font-size: 1.1rem;
    padding: 14px;
  }
  .summary strong { color: var(--gold); }
  .remove-btn {
    background: none;
    border: none;
    color: var(--muted);
    font-size: .85rem;
    cursor: pointer;
    padding: 4px 0;
    margin-top: 8px;
  }
  .remove-btn:hover { color: #ff9d9d; }
  .add-btn {
    width: 100%;
    background: transparent;
    border: 1px dashed var(--accent-dim);
    color: var(--accent);
    border-radius: 10px;
    padding: 12px;
    font-size: 1rem;
    cursor: pointer;
    margin-bottom: 14px;
  }
  .add-btn:hover { border-color: var(--accent); background: rgba(52,211,153,.08); }
  .add-btn:disabled { opacity: .4; cursor: default; }
  .note { color: var(--muted); font-size: .85rem; text-align: center; }
</style>
</head>
<body>
<div class="wrap">
  <header>
    <h1>Unit Price <span class="up">Compare</span></h1>
    <p class="sub">Find the genuinely cheaper grocery option — shelf labels hide the math, this doesn't.</p>
  </header>

  <div id="cards"></div>
  <button class="add-btn" id="addProductBtn">+ Add a product (up to 3)</button>
  <div class="card summary" id="summary">Enter prices and sizes above to compare.</div>
  <p class="note">Prices are compared per 100 g / 100 ml equivalent, normalized to grams and milliliters.</p>
</div>

<script>
(function () {
  'use strict';

  var UNITS = [
    { value: 'g', label: 'g', toBase: 1, kind: 'mass' },
    { value: 'kg', label: 'kg', toBase: 1000, kind: 'mass' },
    { value: 'oz', label: 'oz', toBase: 28.349523125, kind: 'mass' },
    { value: 'lb', label: 'lb', toBase: 453.59237, kind: 'mass' },
    { value: 'ml', label: 'ml', toBase: 1, kind: 'vol' },
    { value: 'l', label: 'L', toBase: 1000, kind: 'vol' }
  ];

  var products = [];
  var nextId = 1;
  var cardsEl = document.getElementById('cards');
  var addBtn = document.getElementById('addProductBtn');
  var summaryEl = document.getElementById('summary');

  function unitByValue(v) {
    for (var i = 0; i < UNITS.length; i++) {
      if (UNITS[i].value === v) return UNITS[i];
    }
    return UNITS[0];
  }

  function addProduct() {
    if (products.length >= 3) return;
    products.push({ id: nextId++, name: '', price: '', size: '', unit: 'g' });
    render();
  }

  function removeProduct(id) {
    products = products.filter(function (p) { return p.id !== id; });
    render();
  }

  function money(n) {
    return '$' + n.toFixed(2);
  }

  function compute(product) {
    var price = parseFloat(product.price);
    var size = parseFloat(product.size);
    if (isNaN(price) || price <= 0 || isNaN(size) || size <= 0) return null;
    var unit = unitByValue(product.unit);
    var baseSize = size * unit.toBase; // grams or milliliters
    var perBase = price / baseSize;    // price per 1 g or 1 ml
    return {
      per100: perBase * 100,
      baseLabel: unit.kind === 'mass' ? 'per 100 g' : 'per 100 ml'
    };
  }

  function recalc() {
    var results = products.map(function (p) { return { id: p.id, name: p.name, result: compute(p) }; });
    var valid = results.filter(function (r) { return r.result !== null; });

    var bestId = null;
    if (valid.length >= 2) {
      bestId = valid.reduce(function (a, b) {
        return a.result.per100 <= b.result.per100 ? a : b;
      }).id;
    }

    products.forEach(function (p) {
      var card = document.getElementById('card-' + p.id);
      var resultEl = document.getElementById('result-' + p.id);
      if (!card || !resultEl) return;
      var r = results.filter(function (x) { return x.id === p.id; })[0];
      if (r.result) {
        resultEl.innerHTML =
          '<span class="ppu">' + money(r.result.per100) + '</span> ' + r.result.baseLabel;
      } else {
        resultEl.innerHTML = '<span class="empty-result">Enter a price and size to compare.</span>';
      }
      var isBest = p.id === bestId;
      card.classList.toggle('cheapest', isBest);
      var badge = card.querySelector('.badge');
      if (isBest) {
        if (!badge) {
          var b = document.createElement('span');
          b.className = 'badge';
          b.textContent = 'CHEAPEST PER UNIT';
          card.insertBefore(b, card.firstChild);
        }
      } else if (badge) {
        badge.remove();
      }
    });

    if (valid.length >= 2) {
      var best = valid.filter(function (r) { return r.id === bestId; })[0];
      var label = best.name.trim() ? best.name.trim() : 'Option ' + (bestId);
      var others = valid.filter(function (r) { return r.id !== bestId; });
      var worst = others.reduce(function (a, b) {
        return a.result.per100 >= b.result.per100 ? a : b;
      });
      var pct = ((worst.result.per100 - best.result.per100) / worst.result.per100 * 100).toFixed(0);
      summaryEl.innerHTML = '<strong>' + escapeHtml(label) + '</strong> is the cheapest at <strong>' +
        money(best.result.per100) + ' ' + best.result.baseLabel +
        '</strong> — ' + pct + '% less per unit than the priciest option.';
    } else {
      summaryEl.textContent = valid.length === 1
        ? 'Add a second product to get a comparison.'
        : 'Enter prices and sizes above to compare.';
    }
  }

  function escapeHtml(s) {
    return String(s)
      .replace(/&/g, '&amp;')
      .replace(/</g, '&lt;')
      .replace(/>/g, '&gt;')
      .replace(/"/g, '&quot;')
      .replace(/'/g, '&#39;');
  }

  function render() {
    cardsEl.innerHTML = '';
    if (products.length === 0) addProduct();
    products.forEach(function (p, idx) {
      var card = document.createElement('div');
      card.className = 'card';
      card.id = 'card-' + p.id;

      var nameLabel = document.createElement('label');
      nameLabel.className = 'name-label';
      nameLabel.textContent = 'Product ' + (idx + 1);
      var nameInput = document.createElement('input');
      nameInput.type = 'text';
      nameInput.placeholder = 'e.g. Oats — house brand';
      nameInput.value = p.name;
      nameInput.addEventListener('input', function () {
        p.name = nameInput.value;
        recalc();
      });

      var row = document.createElement('div');
      row.className = 'row';

      var priceWrap = document.createElement('div');
      var priceLabel = document.createElement('label');
      priceLabel.textContent = 'Price ($)';
      var priceInput = document.createElement('input');
      priceInput.type = 'number';
      priceInput.min = '0';
      priceInput.step = '0.01';
      priceInput.placeholder = 'e.g. 4.99';
      priceInput.value = p.price;
      priceInput.addEventListener('input', function () {
        p.price = priceInput.value;
        recalc();
      });
      priceWrap.appendChild(priceLabel);
      priceWrap.appendChild(priceInput);

      var sizeWrap = document.createElement('div');
      var sizeLabel = document.createElement('label');
      sizeLabel.textContent = 'Size';
      var sizeInput = document.createElement('input');
      sizeInput.type = 'number';
      sizeInput.min = '0';
      sizeInput.step = 'any';
      sizeInput.placeholder = 'e.g. 500';
      sizeInput.value = p.size;
      sizeInput.addEventListener('input', function () {
        p.size = sizeInput.value;
        recalc();
      });
      sizeWrap.appendChild(sizeLabel);
      sizeWrap.appendChild(sizeInput);

      var unitWrap = document.createElement('div');
      var unitLabel = document.createElement('label');
      unitLabel.textContent = 'Unit';
      var unitSelect = document.createElement('select');
      UNITS.forEach(function (u) {
        var opt = document.createElement('option');
        opt.value = u.value;
        opt.textContent = u.label;
        if (u.value === p.unit) opt.selected = true;
        unitSelect.appendChild(opt);
      });
      unitSelect.addEventListener('change', function () {
        p.unit = unitSelect.value;
        recalc();
      });
      unitWrap.appendChild(unitLabel);
      unitWrap.appendChild(unitSelect);

      row.appendChild(priceWrap);
      row.appendChild(sizeWrap);
      row.appendChild(unitWrap);

      var resultDiv = document.createElement('div');
      resultDiv.className = 'result';
      resultDiv.id = 'result-' + p.id;

      card.appendChild(nameLabel);
      card.appendChild(nameInput);
      card.appendChild(row);
      card.appendChild(resultDiv);

      if (products.length > 1) {
        var rm = document.createElement('button');
        rm.className = 'remove-btn';
        rm.textContent = 'Remove this product';
        rm.addEventListener('click', function () { removeProduct(p.id); });
        card.appendChild(rm);
      }

      cardsEl.appendChild(card);
    });
    addBtn.disabled = products.length >= 3;
    recalc();
  }

  addBtn.addEventListener('click', addProduct);

  // Seed two sample rows so the math is visible on first open.
  products.push({ id: nextId++, name: 'Sample Oats A', price: '4.99', size: '500', unit: 'g' });
  products.push({ id: nextId++, name: 'Sample Oats B', price: '8.99', size: '1', unit: 'kg' });
  render();
})();
</script>
</body>
</html>

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