kubernetes-handbook/gitbook/gitbook-plugin-page-toc-button/plugin.js

var gitbook = window.gitbook;
var options = {};

gitbook.events.bind('start', function(e, config) {

	// Save config data
    options = config['page-toc-button'] || {};
	
});

gitbook.events.on('page.change', function() {
	
	// Default config values
	var _maxTocDepth = 2;
	var _minTocSize = 2;

	// Read out config data
	if (options)
	{
		_maxTocDepth = options.maxTocDepth ? options.maxTocDepth : _maxTocDepth;
		_minTocSize = options.minTocSize ? options.minTocSize : _minTocSize;
	};
	
    // Search for headers
	var headerArray = $(".book .body-inner .markdown-section :header");

    // Init variables
	var tocArray = [];
	var tocSize = 0;

    // For each header...
    for (i = 0; i < headerArray.length; i++) {

		var headerElement = headerArray[i];
		var header = $(headerElement);
		var headerId = header.attr("id");
		
        if ((typeof headerId !== typeof undefined) && (headerId !== false)) {

			switch(headerElement.tagName){
				case "H1":
					tocArray.push({
						name: header.text(),
						url: headerId,
						children: []
					});
					tocSize++;
					break;
				case "H2":
					if ((tocArray.length > 0) && (_maxTocDepth >= 1)) {
						tocArray[tocArray.length-1].children.push({
							name: header.text(),
							url: headerId,
							children: []
						});
						tocSize++;
					};
					break;
				case "H3":
					if ((tocArray.length > 0) && (_maxTocDepth >= 2)) {
						if (tocArray[tocArray.length-1].children.length > 0) {
							tocArray[tocArray.length-1].children[tocArray[tocArray.length-1].children.length-1].children.push({
								name: header.text(),
								url: headerId,
								children: []
							});
							tocSize++;
						};
					};
					break;
				default:
					break;
			}
		}	
    };

    // Cancel if not enough headers to show
	if ((tocSize == 0) || (tocSize < _minTocSize)) {
        return;
	}

    // Generate html for button and menu
    var html = "<div class='page-toc-button'><i class='fa fa-bars' aria-hidden='true'></i><div class='page-toc-menu'><ul>";
    for (i = 0; i < tocArray.length; i++) {
        html += "<li><a href='#"+ tocArray[i].url + "'>" + tocArray[i].name + "</a></li>";
        if (tocArray[i].children.length > 0) {
            html += "<ul>"
            for (j = 0; j < tocArray[i].children.length; j++) {
                html += "<li><a href='#" + tocArray[i].children[j].url + "'>"+tocArray[i].children[j].name + "</a></li>";
                if (tocArray[i].children[j].children.length > 0) {
                    html += "<ul>"
                    for (k = 0; k < tocArray[i].children[j].children.length; k++) {
                        html += "<li><a href='#" + tocArray[i].children[j].children[k].url + "'>"+tocArray[i].children[j].children[k].name + "</a></li>";
                    }
                    html += "</ul>"
                }
            }
            html += "</ul>"
        }
    }
    html += "</ul></div></div>";

    // Append generated html to page
	$(".book").append(html)
	
});