I'm currently upgrading my application from Vue.js 1 to Vue.js 2. I have a problem with the following function in my main component:

```
<script>
  export default {
    ready: function listenKeyUp() {
      window.addEventListener('keyup', this.handleKeyUp());
    },

    methods: {
      handleKeyUp(e) {
        if (e.keyCode === 27) {
          this.$router.go({ name: '/' });
        }
      },
    },
  };
</script>

```

My console shows this error: `'window' is not defined`
How is this possible? I don't understand the reason. How to fix this and why is this problem coming up with the new version?

--- EDIT ---
Some additional code:

**main.js:**

```
// Import plugins
import Vue from 'vue';
import VueResource from 'vue-resource';
import VueI18n from 'vue-i18n';

// Import mixins
import api from './mixins/api';

// Import router config
import router from './router';

// Register plugins
Vue.use(VueResource);
Vue.use(VueI18n);
Vue.mixin(api);

// Go
new Vue({
  router,
}).$mount('#app');

```

**index.html:**

```
<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title>New website</title>

        <link rel="shortcut icon" href="/static/favicon.ico" />
        <link rel="apple-touch-icon" href="/static/mobile.png">

        <link rel="stylesheet" href="https://fonts.googleapis.com/css?family=Lato"> 
        <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css">

    </head>
    <body>
        <div id="app">
            <router-view></router-view>
        </div>

        <noscript>
            <div class="container">
                <div class="col-sm-6 col-sm-offset-3">
                    <div class="alert alert-danger">
                        JavaScript is disabled in your web browser!
                    </div>
                </div>
            </div>
        </noscript>

    </body>
</html>

```

**Main component:**

```
<template>
    <div>

        <div class="container">
            <header>
                HEADER HERE
            </header>
        </div>

        <div id="modal" v-if=" $route.name !== 'home' " transition="modal">
            <div id="modal-bg" :to="{ name: 'home' }"></div>
            <div id="modal-container">
                <div id="modal-header">
                    <h2>Modal</h2>
                    <router-link id="modal-close" :to="{ name: 'home' }">X</router-link>
                </div>
                <router-view></router-view>
            </div>
        </div>

        <nav id="primary-navigation">
            <div class="container-fluid">
                <div class="row">
                    NAV HERE
                </div>
            </div>
        </nav>

    </div>
</template>

<script>
  /* SCRIPT PART, SEE TOP OF THIS POST */
</script>

<style lang="scss">
  /* CSS */
</style>

```