Custom elements in iteration require ‘v-bind:key’ directives

There are multiple ways to solve your problem :

1. You want to iterate on a template :
   You have to put a key on all elements in your template because you can not put a key on a template: <template> cannot be keyed. Place the key on real elements instead.

<template v-for="(project, index) in existingProjects">
    <span :key="project.projectId">foo</span>
    <div :key="project.projectId">bar</div>
</template>

2. You can iterate on something else than a template : You just put the key on the parent html tag.

<div v-for="(project, index) in existingProjects" :key="project.projectId">
    <span>foo</span>
    <div>bar</div>
</div>