.local/share/jupyter/nbextensions/snippets_menu/main.js

define([
    "require",
    "jquery",
    "base/js/namespace",
    "./snippets_submenu_python",
    "./snippets_submenu_markdown",
], function (requirejs, $, Jupyter, python, markdown) {
    "use strict";

    var mod_name = 'snippets_menu';
    var mod_log_prefix = mod_name + '[' + mod_name + ']';

    var python_menus = [
        python.numpy,
        python.scipy,
        python.matplotlib,
        python.sympy,
        python.pandas,
        python.astropy,
        python.h5py,
        python.numba,
        python.python,
    ];

    var default_menus = [
        {
            'name' : 'Snippets',
            'sub-menu-direction' : 'left',
            'sub-menu' : python_menus.concat([markdown]),
        },
    ];
    var options = {
        sibling: undefined, // if undefined, set by cfg.sibling_selector
        menus : [],
        hooks: {
            pre_config: undefined,
            post_config: undefined,
        }
    };

    var includable_submenu_keys = [
        "numpy",
        "scipy",
        "matplotlib",
        "sympy",
        "pandas",
        "astropy",
        "h5py",
        "numba",
        "python",
        "markdown",
    ];
    // default parameters
    var cfg = {
        insert_as_new_cell: false,
        insert_before_sibling: false,
        include_custom_menu: false,
        include_submenu: {}, // default set after this definition
        sibling_selector: '#help_menu',
        top_level_submenu_goes_left: true,
        // The default has to be included here as well as config.yaml
        // because the configurator will not store the default given
        // in config.yaml unless it is changed.  That means that this
        // should be kept up-to-date with whatever goes in
        // config.yaml.
        custom_menu_content: JSON.stringify({
            "name" : "My favorites",
            "sub-menu" : [{
                "name" : "Menu item text",
                "snippet" : [
                    "import something",
                    "",
                    "new_command(3.14)",
                    "other_new_code_on_new_line('with a string!')",
                    "stringy(\"if you need them, escape double quotes with a single backslash\")",
                    "backslashy('This \\ appears as just one backslash in the output')",
                    "backslashy2('Here \\\\ are two backslashes')"
                ]}, {
                    "name" : "TeX can be written in menu labels $\\alpha_W e\\int_0 \\mu \\epsilon$",
                    "snippet" : [
                        "another_new_command(2.78)"
                    ]
                }
            ]
        })
    };
    for (var ii=0; ii< includable_submenu_keys.length; ii++) {
        cfg.include_submenu[includable_submenu_keys[ii]] = true;
    }

    function config_loaded_callback () {
        if (options['pre_config_hook'] !== undefined) {
            options['pre_config_hook']();
        }

        // true => deep
        cfg = $.extend(true, cfg, Jupyter.notebook.config.data.snippets);

        if (cfg.insert_as_new_cell) {
            console.log(mod_log_prefix, "Insertions will insert new cell");
        }

        // If `options.menus` had elements added in custom.js, skip all of this and ignore all remaining options
        if (options.menus.length > 0) {
            console.log(mod_log_prefix, '`options.menus` was created in custom.js; skipping all other configuration.');
        }
        else {
            options.menus = [
                {
                    'name' : 'Snippets',
                    'sub-menu-direction' : cfg.top_level_submenu_goes_left ? 'left' : 'right',
                    'sub-menu' : [],
                },
            ];

            if (cfg.include_custom_menu) {
                var custom_menu_content = JSON.parse(cfg.custom_menu_content);
                console.log(mod_log_prefix,
                            "Inserting custom", custom_menu_content.name, "sub-menu");
                options.menus[0]['sub-menu'].push(custom_menu_content);
            }

            for (var ii=0; ii < includable_submenu_keys.length; ii++) {
                var key = includable_submenu_keys[ii];
                if (cfg.include_submenu[key]) {
                    console.log(mod_log_prefix,
                                "Inserting default", key, "sub-menu");
                    options.menus[0]['sub-menu'].push(key === "markdown" ? markdown : python[key]);
                }
            }
        }

        if (options.hooks.post_config !== undefined) {
            options.hooks.post_config();
        }

        // select correct sibling
        if (options.sibling === undefined) {
            options.sibling = $(cfg.sibling_selector).parent();
            if (options.sibling.length < 1) {
                options.sibling = $("#help_menu").parent();
            }
        }
    }

    function insert_snippet_code (snippet_code) {
        if (cfg.insert_as_new_cell) {
            var new_cell = Jupyter.notebook.insert_cell_above('code');
            new_cell.set_text(snippet_code);
            new_cell.focus_cell();
        }
        else {
            var selected_cell = Jupyter.notebook.get_selected_cell();
            Jupyter.notebook.edit_mode();
            selected_cell.code_mirror.replaceSelection(snippet_code, 'around');
        }
    }

    function callback_insert_snippet (evt) {
        // this (or event.currentTarget, see below) always refers to the DOM
        // element the listener was attached to - see
        // http://stackoverflow.com/questions/12077859
        insert_snippet_code($(evt.currentTarget).data('snippet-code'));
    }

    function build_menu_element (menu_item_spec, direction) {
        // Create the menu item html element
        var element = $('<li/>');

        if (typeof menu_item_spec == 'string') {
            if (menu_item_spec != '---') {
                console.log(mod_log_prefix,
                    'Don\'t understand sub-menu string "' + menu_item_spec + '"');
                return null;
            }
            return element.addClass('divider');
        }

        var a = $('<a/>')
            .attr('href', '#')
            .html(menu_item_spec.name)
            .appendTo(element);
        if (menu_item_spec.hasOwnProperty('snippet')) {
            var snippet = menu_item_spec.snippet;
            if (typeof snippet == 'string' || snippet instanceof String) {
                snippet = [snippet];
            }
            a.attr({
                'title' : "", // Do not remove this, even though it's empty!
                'data-snippet-code' : snippet.join('\n'),
            })
            .on('click', callback_insert_snippet)
            .addClass('snippet');
        }
        else if (menu_item_spec.hasOwnProperty('internal-link')) {
            a.attr('href', menu_item_spec['internal-link']);
        }
        else if (menu_item_spec.hasOwnProperty('external-link')) {
            a.empty();
            a.attr({
                'target' : '_blank',
                'title' : 'Opens in a new window',
                'href' : menu_item_spec['external-link'],
            });
            $('<i class="fa fa-external-link menu-icon pull-right"/>').appendTo(a);
            $('<span/>').html(menu_item_spec.name).appendTo(a);
        }

        if (menu_item_spec.hasOwnProperty('sub-menu')) {
            element
                .addClass('dropdown-submenu')
                .toggleClass('dropdown-submenu-left', direction === 'left');
            var sub_element = $('<ul class="dropdown-menu"/>')
                .toggleClass('dropdown-menu-compact', menu_item_spec.overlay === true) // For space-saving menus
                .appendTo(element);

            var new_direction = (menu_item_spec['sub-menu-direction'] === 'left') ? 'left' : 'right';
            for (var j=0; j<menu_item_spec['sub-menu'].length; ++j) {
                var sub_menu_item_spec = build_menu_element(menu_item_spec['sub-menu'][j], new_direction);
                if(sub_menu_item_spec !== null) {
                    sub_menu_item_spec.appendTo(sub_element);
                }
            }
        }

        return element;
    }

    function menu_setup (menu_item_specs, sibling, insert_before_sibling) {
        for (var i=0; i<menu_item_specs.length; ++i) {
            var menu_item_spec;
            if (insert_before_sibling) {
                menu_item_spec = menu_item_specs[i];
            } else {
                menu_item_spec = menu_item_specs[menu_item_specs.length-1-i];
            }
            var direction = (menu_item_spec['menu-direction'] == 'left') ? 'left' : 'right';
            var menu_element = build_menu_element(menu_item_spec, direction);
            // We need special properties if this item is in the navbar
            if ($(sibling).parent().is('ul.nav.navbar-nav')) {
                menu_element
                    .addClass('dropdown')
                    .removeClass('dropdown-submenu dropdown-submenu-left');
                menu_element.children('a')
                    .addClass('dropdown-toggle')
                    .attr({
                        'data-toggle' : 'dropdown',
                        'aria-expanded' : 'false'
                    });
            }

            // Insert the menu element into DOM
            menu_element[insert_before_sibling ? 'insertBefore': 'insertAfter'](sibling);

            // Make sure MathJax will typeset this menu
            window.MathJax.Hub.Queue(["Typeset", window.MathJax.Hub, menu_element[0]]);
        }
    }

    function load_ipython_extension () {
        // Add our css to the notebook's head
        $('<link/>', {
            rel: 'stylesheet',
            type:'text/css',
            href: requirejs.toUrl('./snippets_menu.css')
        }).appendTo('head');

        // Arrange the menus as given by the configuration
        Jupyter.notebook.config.loaded.then(
            config_loaded_callback
        ).then(function () {
            // Parse and insert the menu items
            menu_setup(options.menus, options.sibling, cfg.insert_before_sibling);
        });
    }

    return {
        // Handy functions
        load_ipython_extension : load_ipython_extension,
        menu_setup : menu_setup,

        // Default menus
        python : python,
        python_menus : python_menus,
        markdown : markdown,
        default_menus : default_menus,

        // Items that could be useful for customization
        options : options,
    };

});