allow downloading individual files from bundle

static/js/download-landing.js

@@ -0,0 +1,26 @@
+document.addEventListener('DOMContentLoaded', () => {
+    const downloadCodeInput = document.getElementById('download_code_input');
+    const downloadButton = document.getElementById('download_button');
+    const downloadForm = document.getElementById('download_form');
+    downloadCodeInput.addEventListener('beforeinput', (e) => {
+        if (/^[a-zA-Z0-9-]+$/.test(e.data)) { return; }
+        e.preventDefault();
+        if (e.data === ' ') {
+            downloadCodeInput.value += '-';
+        }
+    });
+    const disableEnableDownload = () => { downloadButton.disabled = (downloadCodeInput.value === ''); };
+    disableEnableDownload();
+    downloadCodeInput.addEventListener('input', disableEnableDownload);
+    downloadForm.addEventListener('submit', (e) => {
+        if (downloadCodeInput.value === '') {
+            e.preventDefault();
+        } else {
+            setTimeout(() => {
+                downloadCodeInput.value = '';
+                downloadButton.disabled = true;
+            }, 0);
+        }
+    });
+    downloadCodeInput.focus();
+});