返回顶部按钮

给页面右下角添加返回顶部按钮
换行
// ==UserScript==
// @name         返回顶部按钮
// @namespace    https://github.com/nameldk/user-script
// @version      0.6
// @description  给页面右下角添加返回顶部按钮
// @author       nameldk
// @match        *://*/*
// @run-at       document-body
// @grant        none
// ==/UserScript==

(function () {
    'use strict';
    var a = document.createElement('a');
    if (!a) return;
    a.href = "javascript:;";
    a.text = "TOP";
    a.style.position = "fixed";
    a.style.right = "5%";
    a.style.bottom = "25%";
    a.style.fontSize = "20px";
    a.style.textDecoration = "none";
    a.style.zIndex = 9999;
    a.style.display = "none";
    document.querySelector("body").appendChild(a);

    var enterRightBottom = 0;
    var leaveTop = 0;

    function showHide() {
        if (leaveTop && enterRightBottom) {
            a.style.display = "block";
        } else {
            a.style.display = "none";
        }
    }

    function animate({
        timing,
        draw,
        duration
    }) {
        let start = performance.now();

        requestAnimationFrame(function animate(time) {
            // timeFraction goes from 0 to 1
            let timeFraction = (time - start) / duration;
            if (timeFraction > 1) timeFraction = 1;

            // calculate the current animation state
            let progress = timing(timeFraction)

            draw(progress); // draw it

            if (timeFraction < 1) {
                requestAnimationFrame(animate);
            }

        });
    }

    window.addEventListener("mousemove", function (e) {
        enterRightBottom = e.clientX > window.innerWidth / 4 * 3 && e.clientY > window.innerHeight / 3 * 2;
        showHide();
    });

    window.addEventListener("scroll", function () {
        leaveTop = (+(document.body.scrollTop || document.documentElement.scrollTop) > 100);
        showHide();
    });

    a.addEventListener("click", function () {
        var height = window.scrollY;
        if (height === 0) return;
        animate({
            timing: function (timeFraction) {
                return 0.5 - Math.cos(timeFraction * Math.PI) / 2;
            },
            draw: function (progress) {
                window.scroll(0, height * (1 - progress));
            },
            duration: 200
        });
    });

})();