How to making sure at least one checkbox is checked using vuejs - vue.js

Question

I would like to guarantee that at least one checkboxes are checked and the price are correct calculated.
https://jsfiddle.net/snoke/1xrzy57u/1/
methods: {
calc: function (item) {
item.isChecked = !item.isChecked
this.total = 0;
for (i = 0; i < this.items.length; i++) {
if(this.items[i].isChecked === true) {
this.total += this.items[i].price;
}
}
// fullPackagePrice
if(this.items[0].isChecked === true && this.items[1].isChecked === true && this.items[2].isChecked === true) {
this.total = this.fullPackagePrice;
}
// Trying to guarantee that have at least one checkbox checked
if(this.items[0].isChecked === false && this.items[1].isChecked === false && this.items[2].isChecked === false) {
this.total = this.items[0].price;
this.items[0].isChecked = true;
}
}
}

Answer 1

A good fit for this would be using computed properties instead of a method.
Read more about these here: https://v2.vuejs.org/v2/guide/computed.html#Computed-Properties
A computed property observes all referenced data and when one piece changes, the function is re-run and re-evaluated.
What you could do is first create a allowCheckout computed property like this:
allowCheckout() {
return this.items[0].isChecked || this.items[1].isChecked || this.items[2].isChecked;
}
You will then use it within the button like this:
<button :disabled="allowCheckout"...
This will disable the button when no items are checked.
Next, you'll also want to create a second computed property for the total price
totalPrice() {
// Perform similar checking here to update this.total
}
Lastly, you'll want to change your checkboxes to no longer use v-on:change but to instead use v-model for the relevant parameter for each.
This way your checkbox status will be bound to the true/falseness of the variables.

Answer 2

If you still want to go with your method, you can implement at like shown in this updated fiddle and set a variable atLeastOneItemIsChecked like this:
this.atLeastOneItemIsChecked = this.items.find(item => item.isChecked) !== undefined
Do not force the user to always check a checkbox. Instead, display a hint and disable the button using :disable and tailwind css resulting in this: