Prevent Vue Multiple Select to Store an Empty Array - vue.js

Question

I want this select multiple to pre-select one option, and not be able to deselect all options.
Whenever the last selected option is deselected it should be reselected. In other words when the user tries to deselect the last selected option it should visually not be deselected.
<template>
<b-select
if="Object.keys(doc).length !== 0 /* wait until firebase has loaded */"
:options="computedOptions"
v-model="model"
multiple
#input="onChange"
/>
</template>
<script>
//import Vue from 'vue'
import { fb } from "../fbconf";
export default {
name: "MyMultiSelect",
props: {
doc: Object, // firestore document
},
data() {
return {
options: []
};
},
firestore() {
var options = fb.db.collection("options");
return {
options: options
};
},
computed: {
computedOptions: function() {
return this.options.map(function(option) {
return {
text: option.name,
value: option.id
};
});
},
// to make sure mySelectedOptions is an array, before this.doc is loaded
// I use the following custom model
// because not using 'get' below causes a warning:
// [Vue warn]: <select multiple v-model="localValue"> expects an Array value for its binding, but got Undefined
model: {
get: function() {
if (!this.doc.hasOwnProperty('mySelectedOptions')) return []; // empty array before this.doc is loaded
else return this.doc['mySelectedOptions'];
},
set: function(newValue) {
// here I can prevent the empty array from being stored
// but visually the user can deselect all options, which is bad UX
//if (Array.isArray(newValue) && newValue.length > 0) this.doc['mySelectedOptions'] = newValue;
}
},
},
methods: {
onChange: function(newValue){
// I can manually store the array as I want here
// but I cannot in any way prevent the user from deselecting all options
if (Array.isArray(newValue) && newValue.length > 0) this.doc['mySelectedOptions'] = newValue;
else {
// none of these reselects the last selected option
var oldValue = this.doc['mySelectedOptions'];
this.doc['mySelectedOptions'] = this.doc['mySelectedOptions'];
//this.$forceUpdate();
//this.$emit("change", newValue);
//Vue.set(this.doc, 'mySelectedOptions', this.doc['mySelectedOptions']);
}
}
}
};
</script>

Answer 1

You could add watcher and when length becomes 0 just add previous value.
watch: {
model(val, oldVal) {
if(val.length == 0 && oldVal.length > 0) {
// take only one item in case there's clear button or etc.
this.model = [oldval[0]];
}
}
}