client: dragged-link helper module

1 files changed, 62 insertions, 0 deletions

diff --git a/src/static/js/client/dragged-link.js b/src/static/js/client/dragged-link.js
new file mode 100644
index 00000000..56021e7f
--- /dev/null
+++ b/src/static/js/client/dragged-link.js
@@ -0,0 +1,62 @@
+/* eslint-env browser */
+
+export const info = {
+  id: `draggedLinkInfo`,
+
+  state: {
+    latestDraggedLink: null,
+    observedLinks: new WeakSet(),
+  },
+};
+
+export function getPageReferences() {
+  // First start handling all the links that currently exist.
+
+  for (const a of document.getElementsByTagName('a')) {
+    observeLink(a);
+    addDragListener(a);
+  }
+
+  // Then add a mutation observer to track new links.
+
+  const observer = new MutationObserver(records => {
+    for (const record of records) {
+      for (const node of record.addedNodes) {
+        if (node.nodeName !== 'A') continue;
+        observeLink(node);
+      }
+    }
+  });
+
+  observer.observe(document.body, {
+    subtree: true,
+    childList: true,
+  });
+}
+
+export function getLatestDraggedLink() {
+  const {state} = info;
+
+  if (state.latestDraggedLink) {
+    return state.latestDraggedLink.deref() ?? null;
+  } else {
+    return null;
+  }
+}
+
+function observeLink(link) {
+  const {state} = info;
+
+  if (state.observedLinks.has(link)) return;
+
+  state.observedLinks.add(link);
+  addDragListener(link);
+}
+
+function addDragListener(link) {
+  const {state} = info;
+
+  link.addEventListener('dragstart', _domEvent => {
+    state.latestDraggedLink = new WeakRef(link);
+  });
+}