Nuxt/Vue/Bootstrap-vue shrink navbar on scroll - vue.js

Question

Learning Vue with Nuxt. Want to change navbar classes depending on the page scroll position.
Looked in several places, but haven't found a working solution.
Here's what I have to work with:
``` default.vue
<template lang="pug">
div(v-on:scroll="shrinkNav", v-on:click="shrinkNav")
b-navbar.text-center(toggleable="sm" type="light" sticky v-b-scrollspy)
#myNav.mx-auto.bg-white
b-navbar-toggle(target="nav_collapse")
b-navbar-brand.mx-auto(href="#")
| Example.org
b-collapse#nav_collapse.mx-auto(is-nav='')
b-navbar-nav(justified, style="min-width: 600px").vertical-center
b-nav-item.my-auto(href='#home') Home
b-nav-item.my-auto(href='/how') How
i.fab.fa-earlybirds.fa-2x.mt-2.mb-3
b-nav-item.my-auto(href='/values') Values
b-nav-item.my-auto(href='/join-us') Join Us
#content.container(v-on:scroll="shrinkNav", v-on:click="shrinkNav")
nuxt
nuxt
</template>
<script>
// resize navbar on scroll
export default {
methods: {
shrinkNav() {
var nav = document.getElementById('nav')
var content = document.getElementById('content')
if (nav && content) {
if(content.scrollTop >= 150) {
nav.classList.add('shrink')
} else {
nav.classList.remove('shrink')
}
}
console.log(document.documentElement.scrollTop || document.body.scrollTop)
}
}
}
</script>
```
shrinkNav runs twice on click, but nothing on scroll. What is the Vue/Nuxt way to do this?

Answer 1

In your .vue:
<template> section:
<nav id="nav" class="navbar is-transparent is-fixed-top">
<script> section:
export default {
mounted() {
this.$nextTick(function(){
window.addEventListener("scroll", function(){
var navbar = document.getElementById("nav");
var nav_classes = navbar.classList;
if(document.documentElement.scrollTop >= 150) {
if (nav_classes.contains("shrink") === false) {
nav_classes.toggle("shrink");
}
}
else {
if (nav_classes.contains("shrink") === true) {
nav_classes.toggle("shrink");
}
}
})
})
},
}
Live Demo on codesandbox

Answer 2

Ok, here's a solution using Plugins. There may be a better way:
1) Define a directive in plugins/scroll.js
``` javascript
// https://vuejs.org/v2/cookbook/creating-custom-scroll-directives.html#Base-Example
import Vue from 'vue'
Vue.directive('scroll', {
inserted: function (el, binding) {
let f = function (evt) {
if (binding.value(evt, el)) {
window.removeEventListener('scroll', f)
}
}
window.addEventListener('scroll', f)
}
})
```
2) Add plugin to project in nuxt.config.js
``` javascript
module.exports = {
head: { },
plugins: [
{ src: '~/plugins/scroll.js', },
]
}
```
3) Use the v-scroll directive to define custom behavior in menu in /layouts/default.vue
``` javascript
<template lang="pug">
div(v-scroll="shrinkNav")
b-navbar.text-center(toggleable="sm" type="light" sticky)
#myNav.mx-auto.bg-white
b-navbar-toggle(target="nav_collapse")
b-navbar-brand.mx-auto(href="/#home") Example.org
b-collapse#nav_collapse.mx-auto(is-nav='')
b-navbar-nav(justified, style="min-width: 600px").vertical-center
b-nav-item.my-auto(to='/#home') Home
#content.container
nuxt
</template>
<script>
export default {
methods: {
shrinkNav() {
var scrollPosition = document.documentElement.scrollTop || document.body.scrollTop
var nav = document.getElementById('myNav')
console.log(scrollPosition, nav)
if(scrollPosition >= 150) {
nav.classList.add('shrink')
} else {
nav.classList.remove('shrink')
}
},
},
}
</script>
<style>
nav.navbar {
margin: 0;
padding: 0;
}
#myNav {
border-radius: 0 0 10px 10px;
border: 2px solid purple;
border-top: none;
}
#myNav.shrink {
border: none;
}
</style>
```