I'm trying to get the height of the window on resize, but I keep getting the error ReferenceError: calcOfSliderHeight is not defined.

Could anyone let me know what's going on? Here's my code

let example = new Vue({
    el: '#example',
    data() {
        return {
            pageIndex: 2,
            posTop: 0,
            posTop2: 0,
        }
    },
    methods: {
        calcOfSliderHeight() {
            let _this = this;
            _this.posTop = (_this.pageIndex - 1) * window.innerHeight
        },
        calcOfSliderHeight2() {
            let _this = this;
            _this.posTop2 = (_this.pageIndex - 3) * window.innerHeight
        },
    },
    mounted: function() {
        let _this = this;

        window.addEventListener('resize', function() {
            calcOfSliderHeight()
            calcOfSliderHeight2()
        });

        _this.posTop = calcOfSliderHeight();
        _this.posTop2 = calcOfSliderHeight2();
    }
});