Simplified and fixed caching issue

ReactNativeClient/lib/Cache.js

@@ -0,0 +1,36 @@
+class Cache {
+
+	async getItem(name) {
+		let output = null;
+		try {
+			const storage = await Cache.storage();
+			output = await storage.getItem(name);
+		} catch (error) {
+			console.info(error);
+			// Defaults to returning null
+		}
+		return output;
+	}
+
+	async setItem(name, value, ttl = null) {
+		try {
+			const storage = await Cache.storage();
+			const options = {};
+			if (ttl !== null) options.ttl = ttl;
+			await storage.setItem(name, value, options);
+		} catch (error) {
+			// Defaults to not saving to cache
+		}
+	}
+
+}
+
+Cache.storage = async function() {
+	if (Cache.storage_) return Cache.storage_;
+	Cache.storage_ = require('node-persist');
+	const osTmpdir = require('os-tmpdir');
+	await Cache.storage_.init({ dir: osTmpdir() + '/joplin-cache', ttl: 1000 * 60 });
+	return Cache.storage_;
+}
+
+module.exports = Cache;