Почему метод Vue.js срабатывает дважды?

var demo = new Vue({
    el: '#demo',
    data: {
        gridData: null,
        end : false
    },
    methods: {
        scroll: function () {
            window.onscroll = () => {
                if (this.end == false) {
                    let bottomOfWindow = document.documentElement.scrollTop + window.innerHeight === document.documentElement.offsetHeight;

                    if (bottomOfWindow) {
                        this.end = true
                        
                        console.log("end")
                        this.upload()
                    }
                    this.end= false
                }
            };
        },
upload: function () {
            this.errored = false;
            this.loading = true;
            axios
                .get('http://localhost:8000')
                .then(response => {

                    this.gridData = response.data.content;
                })
                //.then(response => console.log(response))
                .catch(error => {
                    console.log(error)
                    this.errored = true;
                })


                .finally(() => {
                    this.loading = false;
                    this.time = null;
                });




        },
 mounted: function () {
        this.scroll
}
})