Count.vue

<template>
    <span v-text="count"></span>
</template>

<script>
import inView from 'in-viewport';

export default {
    props: ['to'],

    data() {
        return {
            count: 0,
            interval: null
        };
    },

    computed: {
        increment() {
            return Math.ceil(this.end / 30);
        }
    },

    mounted() {
        inView(this.$el, () => {
            this.interval = setInterval(this.tick, 40);
        });
    },

    methods: {
        tick() {
            if (this.count + this.increment >= this.end) {
                this.count = this.to;

                return clearInterval(this.interval);
            }

            this.count += this.increment;
        }
    }
};
</script>

usage.html

<count :to="1000"></count>

where is 'this.end'

where is 'this.end'

guess it should be this.to. or jeff had a new data 'end' somewhere else.