diff --git a/data_visualization/js/app.js b/data_visualization/js/app.js
new file mode 100644
index 0000000..1d94609
--- /dev/null
+++ b/data_visualization/js/app.js
@@ -0,0 +1,144 @@
+"use strict";
+
+/**
+ * Entry point for the night photography data visualization app.
+ * Coordinates fetching data, initializing chart & gallery, and handling filters.
+ */
+
+(async () => {
+  window.addEventListener('load', initApp);
+
+  /**
+   * Initializes the application by fetching data and rendering UI components.
+   * @returns {Promise<void>}
+   */
+  async function initApp() {
+    const mainContainer = document.querySelector('main');
+    if (!mainContainer) return;
+
+    try {
+      const response = await fetch('/data');
+      if (!response.ok) throw new Error(`HTTP Error ${response.status}`);
+      const data = await response.json();
+
+      const { temperatures = [], images = [] } = data;
+      renderSummary(temperatures, images);
+      renderChart(temperatures);
+      renderGallery(images);
+
+      const filterControls = document.querySelector('.filter-controls');
+      if (filterControls) {
+        filterControls.addEventListener('input', handleFilterChange.bind(null, temperatures, images));
+      }
+    } catch (err) {
+      console.error('App initialization failed:', err);
+      showError(mainContainer, 'Fehler beim Laden der Daten.');
+    }
+  }
+
+  /**
+   * Handles changes in filter controls.
+   * @param {Array} temperatures
+   * @param {Array} images
+   * @param {Event} evt
+   */
+  function handleFilterChange(temperatures, images, evt) {
+    const filterContainer = evt.currentTarget;
+    if (!filterContainer) return;
+
+    const timeRange = filterContainer.querySelector('[name="timeRange"]')?.value || '';
+    const minTemp = parseFloat(filterContainer.querySelector('[name="minTemp"]')?.value) || null;
+    const maxTemp = parseFloat(filterContainer.querySelector('[name="maxTemp"]')?.value) || null;
+
+    const filteredTemps = temperatures.filter(t => {
+      const valueOk = (!minTemp || t.value >= minTemp) && (!maxTemp || t.value <= maxTemp);
+      return valueOk;
+    });
+
+    const filteredImages = images.filter(i => {
+      const relatedTemp = temperatures.find(t => t.timestamp === i.timestamp);
+      if (!relatedTemp) return true;
+      return (!minTemp || relatedTemp.value >= minTemp) && (!maxTemp || relatedTemp.value <= maxTemp);
+    });
+
+    renderChart(filteredTemps);
+    renderGallery(filteredImages);
+    renderSummary(filteredTemps, filteredImages);
+  }
+
+  /**
+   * Renders a simple line chart (placeholder logic – to be replaced by visualization module if available).
+   * @param {Array<{timestamp:string,value:number}>} temps
+   */
+  function renderChart(temps) {
+    const chart = document.querySelector('#temperature-chart');
+    if (!chart) return;
+    chart.innerHTML = '';
+
+    const avg = temps.reduce((acc, t) => acc + t.value, 0) / (temps.length || 1);
+
+    const list = document.createElement('ul');
+    list.className = 'chart__list';
+    temps.forEach(t => {
+      const li = document.createElement('li');
+      li.textContent = `${new Date(t.timestamp).toLocaleTimeString()} – ${t.value.toFixed(1)}°C`;
+      list.appendChild(li);
+    });
+
+    const avgDisplay = document.createElement('p');
+    avgDisplay.className = 'chart__avg';
+    avgDisplay.textContent = `Durchschnitt: ${avg.toFixed(1)}°C`;
+
+    chart.appendChild(list);
+    chart.appendChild(avgDisplay);
+  }
+
+  /**
+   * Renders an image gallery.
+   * @param {Array<{filename:string,timestamp:string,metadata:object}>} images
+   */
+  function renderGallery(images) {
+    const gallery = document.querySelector('#image-gallery');
+    if (!gallery) return;
+    gallery.innerHTML = '';
+
+    images.forEach(img => {
+      const imgEl = document.createElement('div');
+      imgEl.className = 'gallery__image-placeholder';
+      imgEl.setAttribute('aria-label', `Bild aufgenommen um ${new Date(img.timestamp).toLocaleString()}`);
+      imgEl.textContent = `[Bild: ${img.filename}]`;
+      gallery.appendChild(imgEl);
+    });
+
+    const count = document.createElement('p');
+    count.className = 'gallery__count';
+    count.textContent = `Anzahl Bilder: ${images.length}`;
+    gallery.appendChild(count);
+  }
+
+  /**
+   * Render a quick summary of available data.
+   * @param {Array} temps
+   * @param {Array} images
+   */
+  function renderSummary(temps, images) {
+    const summary = document.querySelector('#data-summary');
+    if (!summary) return;
+
+    const avgTemp = temps.reduce((acc, t) => acc + t.value, 0) / (temps.length || 1);
+    summary.textContent = `Durchschnittstemperatur: ${avgTemp.toFixed(1)}°C | Bilder: ${images.length}`;
+  }
+
+  /**
+   * Shows an error message in a container.
+   * @param {HTMLElement} container
+   * @param {string} msg
+   */
+  function showError(container, msg) {
+    container.innerHTML = '';
+    const p = document.createElement('p');
+    p.className = 'error';
+    p.textContent = msg;
+    container.appendChild(p);
+  }
+})();
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