first commit

xterminal/source/input/cursor.ts

@@ -0,0 +1,29 @@
+import type { IReactive } from "../base/reactivity";
+
+/**
+ * Get current cursor position in a textbox
+ * https://stackoverflow.com/16105482/get-current-cursor-position-in-a-textbox
+ */
+
+// TODO: compatibility check
+function getCursorPosition<T extends HTMLElement>(field: T): number {
+    if ("selectionStart" in field) {
+        return field.selectionStart as number;
+    }
+    return 0;
+}
+
+export function updateCursor(
+    el: HTMLTextAreaElement,
+    data: IReactive<string>,
+    ptr: IReactive<number>
+) {
+    let pos = getCursorPosition(el);
+    const len = data.value.length;
+    if (pos > len) {
+        pos = len;
+    } else if (pos < 0) {
+        pos = 0;
+    }
+    ptr.value = pos;
+}