[Outdated] Plugin for BetterDiscord. Creates caret to hide image/video previews.

CollapsibleEmbeds.plugin.js

//META{"name":"CollapsibleEmbeds"}*//
/*
 Check for Updates: https://gist.github.com/shtrih/59a8be1f9ff53f0499c2
 How to install:
     1. If you don't have it, get Discord from https://discordapp.com/apps
     2. Download BetterDiscord for your platform on https://betterdiscord.net/home
     3. Push the button «Raw» then Ctrl + S.
     3. Place the plugin in %appdata%\BetterDiscord\plugins\.
     4. Refresh Discord with Ctrl + Shift + R or just restart Discord completely.
     5. Go to the BetterDiscord settings → plugins tab and check plugin.
 */
function CollapsibleEmbeds() {
    this.initiated = false;
    this.oDefaultSettings = {
        defaultCollapsed: false
    };
    this.oSettings = {};

    var that = this,
        oData,
        iDataTTL = 86400 * 7,
        tagCaret = '&nbsp;<a class="embed-toggle" href="#"><span class="Select-arrow"></span></a>',
        handlerCaretClick = function (e, isTriggered) {
            e.stopPropagation();
            var self = $(e.currentTarget),
                message = self.closest('.message'),
                accessory = $('.accessory', message),
                url = self.prev().attr('href'),
                state
            ;

            if (accessory.children('.attachment').length) {
                accessory.children('.embed, .embed-wrapper').toggleClass('CollapsibleEmbeds-hidden');
            }
            else {
                accessory.toggleClass('CollapsibleEmbeds-hidden');
            }
            self.toggleClass('embed-closed');

            if (!isTriggered && url) {
                state = (self.hasClass('embed-closed') ^ that.oSettings['defaultCollapsed'] ? Date.now() : false);
                that.setState(url, state);
            }
        },
        handlerEachLink = function () {
            var self = $(this),
                message = self.closest('.message'),
                accessory = $('.accessory', message)
            ;
            self.addClass('CollapsibleEmbeds-processed');

            // wait other plugins to create embeds
            setTimeout(function () {
                // In some cases here children <noscript> tag, so no need caret (example message: http://store.otaku.ru/catalog/product/48459.html)
                if (accessory.children(':not(noscript)').length) {
                    self.after(tagCaret)
                        .next('.embed-toggle').on('click', handlerCaretClick)
                    ;

                    loadState(self);
                }
            }, 300);
        },
        loadState = function ($link) {
            var url = $link.attr('href');

            if (!!(url && oData[url]) ^ that.oSettings['defaultCollapsed']) {
                $link.next('.embed-toggle').trigger('click', true /* isTriggered*/);
            }
        },
        tagStyles = '<style>\
            .CollapsibleEmbeds-hidden {\
                display: none !important\
            }\
            .message-group .comment .attachment a.CollapsibleEmbeds-processed,\
            .message-group .comment .attachment .embed-toggle{\
                display: inline-block;\
            }\
            .embed-toggle > .Select-arrow {\
                border-color: #0096cf transparent transparent;\
            }\
            .embed-closed > .Select-arrow {\
                border-width: 4px 0 5px 5px;\
                border-color: transparent #0096cf transparent;\
                margin-left: 2px;\
                padding-right: 4px;\
            }\
        </style>',
        cleanData = function () {
            var expireTime = Date.now() - iDataTTL;
            $.each(oData, function (key, value) {
                if (typeof(value) === 'number' && value < expireTime
                    // remove old v1.* values
                    || typeof(value) !== 'number'
                ) {
                    delete oData[key];
                }
            });
        },
        loadSettings = function () {
            that.oSettings = $.extend(
                that.oDefaultSettings,
                JSON.parse(localStorage.getItem('CollapsibleEmbeds-Settings')) || {}
            );
        },
        saveSettings = function () {
            localStorage.setItem('CollapsibleEmbeds-Settings', JSON.stringify(that.oSettings));
        }
    ;

    this.init = function () {
        $('head').append(tagStyles);

        loadSettings();
        oData = JSON.parse(localStorage.getItem('CollapsibleEmbeds-Data')) || {};
        cleanData();
    };

    this.destroy = function () {
        $('.embed-toggle').remove();
        $('.CollapsibleEmbeds-hidden').removeClass('CollapsibleEmbeds-hidden');
    };

    this.process = function ($links) {
        $links.each(handlerEachLink);
    };

    this.apply = function (){
        if (!this.initiated) {
            this.init();
            this.initiated = true;
        }

        var links = $('.message .markup a:not(.CollapsibleEmbeds-processed):not(.embed-toggle),' +
            '.message .attachment a:not(.CollapsibleEmbeds-processed):not(.embed-toggle)');

        this.process(links);

        // Dealing with attachment images
        var attachment_links = $('.message .attachment-image a:not(.CollapsibleEmbeds-processed):not(.embed-toggle)'),
            attachment_fake_link = $('<a/>', {
                target: '_blank'
            }),
            links_to_process = $()
        ;
        attachment_links.each(function () {
            var self = $(this),
                message = self.closest('.message'),
                link = attachment_fake_link
                    .clone()
                    .attr('href', self.attr('href'))
                    .text(self.attr('href').split('/').pop())
            ;

            self.addClass('CollapsibleEmbeds-processed');
            message.find('.markup').append(link);
            links_to_process = links_to_process.add(link);
        });
        this.process(links_to_process);
    };

    this.setState = function (key, value) {
        if (!value) {
            delete oData[key];
        }
        else {
            oData[key] = value;
        }
        localStorage.setItem('CollapsibleEmbeds-Data', JSON.stringify(oData));
    };

    this.setOption = function (key, value) {
        that.oSettings[key] = value;
        saveSettings();
    };
}
CollapsibleEmbeds.prototype.getName = function() {
    return "CollapsibleEmbeds";
};
CollapsibleEmbeds.prototype.getDescription = function() {
    return "Near each link adds a carriage, which allows you to hide image/video preview. It works with \"embed\" plugins.\n";
};
CollapsibleEmbeds.prototype.getVersion = function() {
    return "2.1.1";
};
CollapsibleEmbeds.prototype.getAuthor = function() {
    return "shtrih";
};
CollapsibleEmbeds.prototype.getSettingsPanel = function() {
    if (!this.oSettings)
        this.loadSettings();

    return '<label><input type="checkbox"'+ (this.oSettings['defaultCollapsed'] ? ' checked="checked" ' : '')
        +' onchange="BdApi.getPlugin(\'CollapsibleEmbeds\').setOption(\'defaultCollapsed\', $(this).is(\':checked\'))" /> Collapsed previews by default</label>'
        +'<p>ProTip: Settings will take effect when you switch the channel. No need to restart Discord.</p>';
};

CollapsibleEmbeds.prototype.load = function() {
    console.info("%c[BetterDiscord]" + " %c" + this.getName() + " v" + this.getVersion() + " by " + this.getAuthor() + " loaded.", "color: purple; font-weight: bold;", "");
};
CollapsibleEmbeds.prototype.unload = function() {
    this.destroy();
};
CollapsibleEmbeds.prototype.start = function() {
    this.apply();
};
CollapsibleEmbeds.prototype.stop = function() {
    this.destroy();
};
CollapsibleEmbeds.prototype.onMessage = function() {
    this.apply();
};
CollapsibleEmbeds.prototype.onSwitch = function() {
    this.apply();
};

Life goes on, plans change. I haven't used betterdiscord plugins for a long time. And this plugin was made, first of all, for myself. So don't expect any updates.
There are many people in betterdiscord team with relevant knowledge who are developing plugins. I think you should contact them.