feat: add preserve indent plugin

src/plugins/preserveIndent.js

@@ -0,0 +1,43 @@
+import isKey from "./isKey.js";
+
+const preserveIndent = () => (textareaProps, event) => {
+  const { value, selectionStart, selectionEnd } = textareaProps;
+
+  if (!isKey("enter", event)) {
+    return;
+  }
+
+  if (event.type !== "keydown") {
+    return;
+  }
+
+  const currentLineNumber =
+    value.substring(0, selectionStart).split("\n").length - 1;
+
+  const lines = value.split("\n");
+  const currentLine = lines[currentLineNumber];
+  const matches = /^\s+/.exec(currentLine);
+
+  if (!matches) {
+    return;
+  }
+
+  event.preventDefault();
+  const indent = matches[0];
+  const newLine = "\n";
+
+  const inserted = newLine + indent;
+
+  const newValue =
+    value.substring(0, selectionStart) +
+    inserted +
+    value.substring(selectionEnd);
+
+  return {
+    value: newValue,
+    selectionStart: selectionStart + inserted.length,
+    selectionEnd: selectionStart + inserted.length,
+  };
+};
+
+export default preserveIndent;