修改方法：

修改文件/vendor/flarum/markdown/js/dist/forum.js由于源文件经过编译优化，所以要进行格式化。

以下两处可以参考我的格式进行添加，以添加一个内容回复可见按钮为例

全局变量 S 中增加

reply: {prefix: "[reply]", suffix: "[/reply]", trimFirst: !0},

其中prefix顾名思义为在光标或者选中字段前添加的内容，suffix为在光标或者选中字段后添加的内容

在 F 方法体中的返回值增加

e.add("reply", m(w, {
        title: r("reply"),
        icon: "fas fa-reply",
        onclick: i("reply")
      }), 0)

title是代表对应显示的文字，
icon是按钮的图标
后面的0代表按钮的顺序，越大越在前面

完整代码

添加回复可见按钮可以使用我下面改写完成的代码

//格式化完成的代码 
(() => {
  var t = {
    n: o => {
      var e = o && o.__esModule ? () => o.default : () => o;
      return t.d(e, {a: e}), e
    }, d: (o, e) => {
      for (var r in e) t.o(e, r) && !t.o(o, r) && Object.defineProperty(o, r, {enumerable: !0, get: e[r]})
    }, o: (t, o) => Object.prototype.hasOwnProperty.call(t, o), r: t => {
      "undefined" != typeof Symbol && Symbol.toStringTag && Object.defineProperty(t, Symbol.toStringTag, {value: "Module"}), Object.defineProperty(t, "__esModule", {value: !0})
    }
  }, o = {};
  (() => {
    "use strict";
    t.r(o);
    const e = flarum.core.compat["forum/app"];
    var r = t.n(e);
    const i = flarum.core.compat["common/app"];
    var n = t.n(i);
    const a = flarum.core.compat["common/extend"], c = flarum.core.compat["common/components/TextEditor"];
    var l = t.n(c);
    const s = flarum.core.compat["common/utils/BasicEditorDriver"];
    var d = t.n(s);
    const u = flarum.core.compat["common/utils/styleSelectedText"];
    var f = t.n(u);

    function p(t, o) {
      return p = Object.setPrototypeOf ? Object.setPrototypeOf.bind() : function (t, o) {
        return t.__proto__ = o, t
      }, p(t, o)
    }

    function h(t, o) {
      t.prototype = Object.create(o.prototype), t.prototype.constructor = t, p(t, o)
    }

    const k = flarum.core.compat["common/Component"];
    var y = t.n(k), b = function (t) {
      function o() {
        return t.apply(this, arguments) || this
      }

      return h(o, t), o.prototype.view = function (t) {
        return m("div", {class: "MarkdownToolbar"}, t.children)
      }, o
    }(y());
    const x = flarum.core.compat["common/helpers/icon"];
    var v = t.n(x);
    const g = flarum.core.compat["common/components/Tooltip"];
    var _ = t.n(g), w = function (t) {
      function o() {
        return t.apply(this, arguments) || this
      }

      h(o, t);
      var e = o.prototype;
      return e.oncreate = function (o) {
        t.prototype.oncreate.call(this, o)
      }, e.view = function () {
        var t = m("button", {
          className: "Button Button--icon Button--link",
          type: "button",
          "data-hotkey": this.attrs.hotkey,
          onkeydown: this.keydown.bind(this),
          onclick: this.attrs.onclick
        }, v()(this.attrs.icon));
        return this.attrs.title ? m(_(), {text: this.attrs.title}, t) : t
      }, e.keydown = function (t) {
        " " !== t.key && "Enter" !== t.key || (t.preventDefault(), this.element.click())
      }, o
    }(y());
    const O = flarum.core.compat["common/utils/ItemList"];
    var T = t.n(O), P = navigator.userAgent.match(/Macintosh/) ? "⌘" : "ctrl", S = {
      header: {prefix: "### "},
      bold: {prefix: "**", suffix: "**", trimFirst: !0},
      reply: {prefix: "[reply]", suffix: "[/reply]", trimFirst: !0},
      italic: {prefix: "_", suffix: "_", trimFirst: !0},
      strikethrough: {prefix: "~~", suffix: "~~", trimFirst: !0},
      quote: {prefix: "> ", multiline: !0, surroundWithNewlines: !0},
      code: {prefix: "`", suffix: "`", blockPrefix: "```", blockSuffix: "```"},
      link: {prefix: "[", suffix: "](https://)", replaceNext: "https://", scanFor: "https?://"},
      image: {prefix: "![", suffix: "](https://)", replaceNext: "https://", scanFor: "https?://"},
      unordered_list: {prefix: "- ", multiline: !0, surroundWithNewlines: !0},
      ordered_list: {prefix: "1. ", multiline: !0, orderedList: !0},
      spoiler: {prefix: ">!", suffix: "!<", blockPrefix: ">! ", multiline: !0, trimFirst: !0},
    }, j = function (t, o) {
      f()(o.el, S[t])
    };

    function I(t, o, e) {
      return function (r) {
        r.key === o && (r.metaKey && "⌘" === P || r.ctrlKey && "ctrl" === P) && (r.preventDefault(), j(t, e))
      }
    }

    function F(t) {
      var o = this, e = "function" == typeof t ? t() : new (T());

      function r(t, o) {
        return n().translator.trans("flarum-markdown.lib.composer." + t + "_tooltip") + (o ? " <" + P + "-" + o + ">" : "")
      }

      var i = function (t) {
        return function () {
          return j(t, o.attrs.composer.editor)
        }
      };
      return e.add("header", m(w, {
        title: r("header"),
        icon: "fas fa-heading",
        onclick: i("header")
      }), 1e3), e.add("bold", m(w, {
        title: r("bold", "b"),
        icon: "fas fa-bold",
        onclick: i("bold")
      }), 900), e.add("italic", m(w, {
        title: r("italic", "i"),
        icon: "fas fa-italic",
        onclick: i("italic")
      }), 800), e.add("strikethrough", m(w, {
        title: r("strikethrough"),
        icon: "fas fa-strikethrough",
        onclick: i("strikethrough")
      }), 700), e.add("reply", m(w, {
        title: r("reply"),
        icon: "fas fa-reply",
        onclick: i("reply")
      }), 0),e.add("quote", m(w, {
        title: r("quote"),
        icon: "fas fa-quote-left",
        onclick: i("quote")
      }), 600), e.add("spoiler", m(w, {
        title: r("spoiler"),
        icon: "fas fa-exclamation-triangle",
        onclick: i("spoiler")
      }), 500), e.add("code", m(w, {
        title: r("code"),
        icon: "fas fa-code",
        onclick: i("code")
      }), 400), e.add("link", m(w, {
        title: r("link"),
        icon: "fas fa-link",
        onclick: i("link")
      }), 300), e.add("image", m(w, {
        title: r("image"),
        icon: "fas fa-image",
        onclick: i("image")
      }), 200), e.add("unordered_list", m(w, {
        title: r("unordered_list"),
        icon: "fas fa-list-ul",
        onclick: i("unordered_list")
      }), 100), e.add("ordered_list", m(w, {
        title: r("ordered_list"),
        icon: "fas fa-list-ol",
        onclick: i("ordered_list")
      }), 0), e
    }

    r().initializers.add("flarum-markdown", (function (t) {
      (0, a.extend)(d().prototype, "keyHandlers", (function (t) {
        t.add("bold", I("bold", "b", this)), t.add("italic", I("italic", "i", this))
      })), l().prototype.markdownToolbarItems ? (0, a.override)(l().prototype, "markdownToolbarItems", F) : l().prototype.markdownToolbarItems = F, (0, a.extend)(l().prototype, "toolbarItems", (function (t) {
        t.add("markdown", m(b, {
          for: this.textareaId, setShortcutHandler: function (t) {
            return shortcutHandler = t
          }
        }, this.markdownToolbarItems().toArray()), 100)
      }))
    }))
  })(), module.exports = o
})();
//# sourceMappingURL=forum.js.map