double exclamation mark

App.vue

<template>
  <div id="app">
    <router-view />
  </div>
</template>

<style>
</style>

<script>
import SettingsHelper from "./store/settings.js";

export default {
  mounted() {
    window.addEventListener("storage", this.onSettingsUpdated);

    let settings = SettingsHelper.readFromLocalStorage();
    this.$store.commit("updateSettings", settings);
  },
  beforeDestroy() {
    window.removeEventListener("storage", this.onSettingsUpdated);
  },
  methods: {
    onSettingsUpdated(event) {
      let settings = SettingsHelper.readFromEvent(event);
      if (!!settings) {
        this.$store.commit("updateSettings", settings);
      }
    }
  }
};
</script>

settings.js

const settingsHelper = {
    // ...
    readFromEvent(event) {
        if (event.key != "settings") {
            return null;
        }
        let settings = JSON.parse(event.newValue);
        if (!this.isSettingsValid(settings)) {
            settings = this.resetSettings();
        }
        return settings;
    }
    // ...
}

export default settingsHelper;