fix: add persistentWritable

Author: jacob-tucker

package-lock.json

@@ -73,6 +73,7 @@
 		"@mateoroldos/svelte.bones": "^1.2.0",
 		"@types/prismjs": "^1.26.0",
 		"cssnano": "^5.1.14",
+		"devalue": "^4.3.2",
 		"js-cookie": "^3.0.5",
 		"prismjs": "^1.29.0"
 	},

package.json

@@ -0,0 +1,49 @@
+import { writable, type Writable } from 'svelte/store';
+import { browser } from '$app/environment';
+import * as devalue from 'devalue';
+import Cookies from 'js-cookie';
+
+function persistentWritable<T>(key: string, defaultValue: T, useCookies: boolean = false) {
+  // Create a writable store.
+  const { subscribe, set, update }: Writable<T> = writable();
+
+  let storedValue: string | undefined | null;
+  // Get stored value.
+  if (browser) {
+    storedValue = useCookies ? Cookies.get(key) : localStorage.getItem(key);
+  }
+
+  // Determine resolved value.
+  const resolvedValue: T | string | null =
+    storedValue === undefined || storedValue === null ? defaultValue : storedValue;
+  if (resolvedValue && isJsonString(resolvedValue)) {
+    set(devalue.parse(resolvedValue as string));
+  } else {
+    set(resolvedValue as T);
+  }
+
+  // Subscribe to changes.
+  subscribe((value) => {
+    // Store the new value.
+    if (browser) {
+      if (useCookies) {
+        Cookies.set(key, value);
+      } else {
+        localStorage.setItem(key, devalue.stringify(value));
+      }
+    }
+  });
+
+  return { subscribe, set, update };
+}
+
+function isJsonString<T>(str: T | string) {
+  try {
+    devalue.parse(str as string);
+  } catch (e) {
+    return false;
+  }
+  return true;
+}
+
+export default persistentWritable;