Fix cache-purging not working

src/common/JsonFileManager.js

@@ -0,0 +1,36 @@
+const fs = require('fs');
+
+class JsonFileManager {
+  constructor(file) {
+    this.jsonFile = file;
+    try {
+      this.json = JSON.parse(fs.readFileSync(file, 'utf-8'));
+    } catch (err) {
+      this.json = {};
+    }
+  }
+
+  writeToFile() {
+    fs.writeFile(this.jsonFile, JSON.stringify(this.json, null, 2), (err) => {
+      if (err) {
+        console.error(err);
+      }
+    });
+  }
+
+  setJson(json) {
+    this.json = json;
+    this.writeToFile();
+  }
+
+  setValue(key, value) {
+    this.json[key] = value;
+    this.writeToFile();
+  }
+
+  getValue(key) {
+    return this.json[key];
+  }
+}
+
+module.exports = JsonFileManager;