1、安装 Tampermonkey

谷歌浏览器翻墙，从chrome扩展应用商店搜索Tampermonkey安装好。

点击油猴插件添加新脚本：

然后就可以在编辑器里写脚本为页面添加侧边目录。

2、脚步代码

思路：
查看简书文章页面的源码，可以发现所有的标题行都放在h1,h2,h3,h4,h5,h6 标签内，所以将页面设计成在文章左侧插入列表, 按标题层级进行缩进，点击进行跳转。
将下面的代码贴进编辑器即可。

// ==UserScript==
// @name         简书网站左侧目录生成
// @namespace    http://tampermonkey.net/
// @version      1.0.0
// @description  简书网站左侧目录生成,支持非h1标题,支持滚动
// ==/UserScript==

(function () {
    'use strict';
    initSidebar('.sidebar', '._2rhmJa');
})();

function initSidebar(sidebarQuery, contentQuery) {
    addAllStyle()
    var body = document.body
    var sidebar = document.querySelector(sidebarQuery)
    // 在 body 标签内部添加 div.sidebar 侧边栏,用于显示文档目录
    if (!sidebar) {
        sidebar = document.createElement('div')
        body.insertBefore(sidebar, body.firstChild)
    }
    sidebar.classList.add('sidebar')
    var content = document.querySelector(contentQuery)
    if (!content) {
        throw ('Error: content not find!')
        return
    }
    content.classList.add('content-with-sidebar');
    var ul = document.createElement('ul')
    ul.classList.add('menu-root')
    sidebar.appendChild(ul)

    var allHeaders = []
    var i = 1
    var headers = [].slice.call(content.querySelectorAll('h' + i++), 1)
    while (!headers.length && i <= 6) {
        headers = Array.from(content.querySelectorAll('h' + i++))
    }
    [].unshift.call(headers, content.querySelector('h1'))
    if (headers.length) {
        [].forEach.call(headers, function (h) {
            var h1 = makeLink(h, 'a', 'h1-link')
            ul.appendChild(h1)
            allHeaders.push(h)
            //寻找h1的子标题
            var h2s = collectHs(h)
            if (h2s.length) {
                [].forEach.call(h2s, function (h2) {
                    allHeaders.push(h2)
                    var h3s = collectHs(h2)
                    h2 = makeLink(h2, 'a', 'h2-link')
                    ul.appendChild(h2)
                    //再寻找 h2 的子标题 h3
                    if (h3s.length) {
                        var subUl = document.createElement('ul')
                        subUl.classList.add('menu-sub')
                        h2.appendChild(subUl)
                            ;[].forEach.call(h3s, function (h3) {
                                allHeaders.push(h3)
                                h3 = makeLink(h3, 'a', 'h3-link')
                                subUl.appendChild(h3)
                            })
                    }
                })
            }
        })
    }
    //增加 click 点击处理,使用 scrollIntoView,增加控制滚动的 flag
    var scrollFlag = 0
    var scrollFlagTimer
    sidebar.addEventListener('click', function (e) {
        e.preventDefault()
        if (e.target.href) {
            scrollFlag = 1
            clearTimeout(scrollFlagTimer)
            scrollFlagTimer = setTimeout(() => scrollFlag = 0, 1500)
            setActive(e.target, sidebar)
            var target = document.getElementById(e.target.getAttribute('href').slice(1))
            target.scrollIntoView({ behavior: 'smooth', block: "center" })
        }
    })
    //监听窗口的滚动和缩放事件
    window.addEventListener('scroll', updateSidebar)
    window.addEventListener('resize', throttle(updateSidebar))
    function updateSidebar() {
        if (scrollFlag)
            return
        var doc = document.documentElement
        var top = doc && doc.scrollTop || document.body.scrollTop
        if (!allHeaders.length) return
        var last
        for (var i = 0; i < allHeaders.length; i++) {
            var link = allHeaders[i]
            if (link.offsetTop > (top + document.body.clientHeight / 2 - 73)) {
                if (!last) { last = link }
                break
            } else {
                last = link
            }
        }
        if (last) {
            setActive(last.id, sidebar)
        }
    }
}

function makeLink(h, tag, className) {
    tag = tag || 'a'
    className = className || ''
    var link = document.createElement('li')
    var text = [].slice.call(h.childNodes).map(function (node) {
        if (node.nodeType === Node.TEXT_NODE) {
            return node.nodeValue
        } else if (['CODE', 'SPAN', 'A'].indexOf(node.tagName) !== -1) {
            return node.textContent
        } else {
            return ''
        }
    }).join('').replace(/\(.*\)$/, '')
    if (!h.id) h.id = IdEscape(text)
    link.innerHTML =
        `<${tag} class="${className}" href="#${h.id}">${htmlEscape(text)}</${tag}>`
    return link
}

function IdEscape(text) {
    return text.replace(/[\s"']/g, '_') //注意这里不加 g 的话就会只匹配第一个匹配,所以会出错
}
function htmlEscape(text) {
    return text
        .replace(/&/g, '&amp;')
        .replace(/"/g, '&quot;')
        .replace(/'/g, '&#39;')
        .replace(/</g, '&lt;')
        .replace(/>/g, '&gt;')
}
function collectHs(h) {
    var childIndexes = []
    var thisTag = h.tagName
    var count = 1
    do {
        var childTag = h.tagName[0] + (parseInt(h.tagName[1]) + count++)
        var next = h.nextElementSibling
        while (next) {
            if (next.tagName[0] == 'H' && next.tagName[1] <= thisTag[1]) {
                break
            }
            else if (next.tagName === childTag) {
                childIndexes.push(next)
            }
            next = next.nextElementSibling
        }
    } while (childTag < 'H6' && childIndexes.length == 0)
    return childIndexes
}

function setActive(id, sidebar) {
    //1.无论对h2还是 h3进行操作,首先都要移除所有的 active 和 current 类,
    var previousActives = sidebar.querySelectorAll(`.active`)
        ;[].forEach.call(previousActives, function (h) {
            h.classList.remove('active')
        })
    previousActives = sidebar.querySelectorAll(`.current`)
        ;[].forEach.call(previousActives, function (h) {
            h.classList.remove('current')
        })
    //获取要操作的目录节点
    var currentActive = typeof id === 'string'
        ? sidebar.querySelector('a[href="#' + id + '"]')
        : id
    if (currentActive.classList.contains('h2-link') != -1) {
        //2. 若为 h2,则添加 active 和 current
        currentActive.classList.add('active', 'current')
    }
    if ([].indexOf.call(currentActive.classList, 'h3-link') != -1) {
        //3. 若为 h3,则添加 active 且对其父目录添加 current
        currentActive.classList.add('active')
        var parent = currentActive
        while (parent && parent.tagName != 'UL') {
            parent = parent.parentNode
        }
        parent.parentNode.querySelector('.h2-link').classList.add('current', 'active')
    }
    //左侧目录太长时的效果
    currentActive.scrollIntoView({ behavior: 'smooth' })
}

function addAllStyle(highlightColor) {
    highlightColor = highlightColor || "#c7254e"
    var sheet = newStyleSheet()

    function newStyleSheet() {
        var style = document.createElement("style");
        // 对WebKit hack :(
        style.appendChild(document.createTextNode(""));
        // 将 <style> 元素加到页面中
        document.head.appendChild(style);
        return style.sheet;
    }
    var position = 0

    function addStyle(str) {
        sheet.insertRule(str,position++);
    }
    addStyle(`.sidebar{position:fixed;    z-index: 10;
        top: 61px;
        left: 0;
        bottom: 0;
        overflow-x: hidden;
        overflow-y: auto;
        padding: 40px 20px 60px 30px;
        max-width: 310px;
    }`)
    addStyle(`.menu-root { list-style:none; text-align:left }`)
    addStyle(`.menu-root .h1-link{
        display:inline-block;
        color:rgb(44, 62, 80);
        font-family:"source sans pro", "helvetica neue", Arial, sans-serif;
        font-size:17.55px;
        font-weight:600;
        height:22px;
        line-height:22.5px;
        list-style-type:none;
        margin-block-end:11px;
        margin-block-start:11px;
    }`)
    addStyle(`.menu-root .h2-link:hover {
        border-bottom: 2px solid ${highlightColor};
    }`)
    addStyle(`.menu-root .h2-link.current+.menu-sub{
        display:block;
    }`)
    addStyle(`.menu-root .h2-link{
        color:rgb(127,140,141);
        cursor:pointer;
        font-family:"source sans pro", "helvetica neue", Arial, sans-serif;
        font-size:15px;
        height:auto;
        line-height:22.5px;
        list-style-type:none;
        text-align:left;
        text-decoration-color:rgb(127, 140, 141);
        text-decoration-line:none;
        text-decoration-style:solid;
        margin-left:12.5px;
    }`)
    addStyle(`.menu-sub {
        padding-left:25px;
        list-style:none;
        display:none;
    }`)
    addStyle(`.menu-sub .h3-link{
        color:#333333;
        cursor:pointer;
        display:inline;
        font-family:"source sans pro", "helvetica neue", Arial, sans-serif;
        font-size:12.75px;
        height:auto;
        line-height:19.125px;
        list-style-type:none;
        text-align:left;
        text-decoration-color:rgb(52, 73, 94);
        text-decoration-line:none;
        text-decoration-style:solid;
    }`)
    addStyle(`@media only screen and (max-width : 1300px){
        .content-with-sidebar {
            margin-left:310px !important;
        }
    }`)
    addStyle(`.sidebar .active{
        color:${highlightColor};
        font-weight:700;
    }`)
}

function throttle(fn, interval = 300) {
    let canRun = true;
    return function () {
        if (!canRun) return;
        canRun = false;
        setTimeout(() => {
            fn.apply(this, arguments);
            canRun = true;
        }, interval);
    };
}

3、效果