Vue 2 – Mutating props vue-warn

I started https://laracasts.com/series/learning-vue-step-by-step series. I stopped on the lesson Vue, Laravel, and AJAX with this error:

vue.js:2574 [Vue warn]: Avoid mutating a prop directly since the value will be overwritten whenever the parent component re-renders. Instead, use a data or computed property based on the prop’s value. Prop being mutated: “list” (found in component )

I have this code in main.js

Vue.component('task', {
    template: '#task-template',
    props: ['list'],
    created() {
        this.list = JSON.parse(this.list);
    }
});
new Vue({
    el: '.container'
})

I know that the problem is in created() when I overwrite the list prop, but I am a newbie in Vue, so I totally don’t know how to fix it. Anyone have an idea how (and please explain why) to fix it?