countdown.vue

<template>
    <div>
        <div class="card text-white bg-info mb-3" v-if="seconds">
            <div class="card-body">
                <h2>{{ countdown }}</h2>
            </div>
        </div>
    </div>
</template>

<script>
    import * as moment from 'moment';
    export default {
        name: 'CountDown',
        props: {
            seconds: {
                type: Number,
                required: true
            }
        },
        data () {
            return {
                countdown: null,
                expires_in: null,
                interval: null,
            }
        },
        mounted () {
            this.countdown = moment.utc(this.seconds).format('HH:mm:ss');
            this.expires_in = this.seconds;
        }
    }
</script>