首先在data定义变量：

data() {
        return {
            screenWidth: document.body.clientWidth
        };
    },

监听窗口大小变化：

mounted() {
        const that = this;
        window.onresize = () => (() => {
            window.screenWidth = document.body.clientWidth;
            that.screenWidth = window.screenWidth;
        })();
    },
    watch: {
        screenWidth(val) {
            // 为了避免频繁触发resize函数导致页面卡顿，使用定时器
            if (!this.timer) {
                // 一旦监听到的screenWidth值改变，就将其重新赋给data里的screenWidth
                this.screenWidth = val;
                this.timer = true;
                const that = this;
                setTimeout(function () {
                    that.sjcount(that.screenWidth);//窗口大小变化后执行的方法
                    that.reload();//窗口大小变化后执行的方法
                    that.timer = false;
                }, 10);
            }
        }
    }

methods: {
reload() {
            this.isAlive = false;
            this.$nextTick(function () {
                this.isAlive = true;
            });
        },
        sjcount(screewidth) {
            if (screewidth >= 1920) {
                this.numeral = 8;
            } else if (screewidth >= 1680) {
                this.numeral = 7;
            } else if (screewidth >= 1600) {
                this.numeral = 5;
            } else if (screewidth >= 1280) {
                this.numeral = 5;
            } else if (screewidth >= 1024) {
                this.numeral = 4;
            }
        },

}