'window' is not defined in Vue.js 2
The safest place to use browser references is the mounted() lifecycle hook. Especially if you're using a SSR setup like Nuxt.js or similar.
Try putting the listener in your created() method
You're also going to be losing context on your this so use a lexical fat arrow to preserve the context
// rest of exportcreated() { // make an event listener and pass the right `this` through window.addEventListener('keyup', (event) => { // if the key is escape if (event.keyCode === 27) { // due to `=>` this is the this you're expecting this.keyHandler() } }},methods: { keyHandler() { // this *should* be the right this this.$router.go({ name: '/' }) }}// rest of exportCompletely untested but it should work (vue 2.x)