Convert HTML into Markdown with JavaScript Turndown.

// --------------------------------------------------------------------------
// Turndown
// Convert HTML into Markdown with JavaScript.
//
// Homepage: https://github.com/domchristie/turndown
// Source: https://unpkg.com/turndown@7.0.0/dist/turndown.js
// Demo: https://domchristie.github.io/turndown/
// Copyright: Turndown is copyright (C) 2017+ Dom Christie and released under the MIT license.
// --------------------------------------------------------------------------

// --------------------------------------------------------------------------
// Usage
// --------------------------------------------------------------------------
// For Node.js
// var TurndownService = require("turndown");
//
// For browser
// <script src="https://unpkg.com/turndown/dist/turndown.js"></script>
//
// var turndownService = new TurndownService();
// var markdown = turndownService.turndown("<h1>Hello world!</h1>");
// --------------------------------------------------------------------------

var TurndownService = (function () {
    "use strict";

    function extend(destination) {
        for (var i = 1; i < arguments.length; i++) {
            var source = arguments[i];
            for (var key in source) {
                if (source.hasOwnProperty(key)) destination[key] = source[key];
            }
        }
        return destination;
    }

    function repeat(character, count) {
        return Array(count + 1).join(character);
    }

    var blockElements = [
        "ADDRESS",
        "ARTICLE",
        "ASIDE",
        "AUDIO",
        "BLOCKQUOTE",
        "BODY",
        "CANVAS",
        "CENTER",
        "DD",
        "DIR",
        "DIV",
        "DL",
        "DT",
        "FIELDSET",
        "FIGCAPTION",
        "FIGURE",
        "FOOTER",
        "FORM",
        "FRAMESET",
        "H1",
        "H2",
        "H3",
        "H4",
        "H5",
        "H6",
        "HEADER",
        "HGROUP",
        "HR",
        "HTML",
        "ISINDEX",
        "LI",
        "MAIN",
        "MENU",
        "NAV",
        "NOFRAMES",
        "NOSCRIPT",
        "OL",
        "OUTPUT",
        "P",
        "PRE",
        "SECTION",
        "TABLE",
        "TBODY",
        "TD",
        "TFOOT",
        "TH",
        "THEAD",
        "TR",
        "UL"
    ];

    function isBlock(node) {
        return is(node, blockElements);
    }

    var voidElements = [
        "AREA",
        "BASE",
        "BR",
        "COL",
        "COMMAND",
        "EMBED",
        "HR",
        "IMG",
        "INPUT",
        "KEYGEN",
        "LINK",
        "META",
        "PARAM",
        "SOURCE",
        "TRACK",
        "WBR"
    ];

    function isVoid(node) {
        return is(node, voidElements);
    }

    function hasVoid(node) {
        return has(node, voidElements);
    }

    var meaningfulWhenBlankElements = [
        "A",
        "TABLE",
        "THEAD",
        "TBODY",
        "TFOOT",
        "TH",
        "TD",
        "IFRAME",
        "SCRIPT",
        "AUDIO",
        "VIDEO"
    ];

    function isMeaningfulWhenBlank(node) {
        return is(node, meaningfulWhenBlankElements);
    }

    function hasMeaningfulWhenBlank(node) {
        return has(node, meaningfulWhenBlankElements);
    }

    function is(node, tagNames) {
        return tagNames.indexOf(node.nodeName) >= 0;
    }

    function has(node, tagNames) {
        return (
            node.getElementsByTagName &&
            tagNames.some(function (tagName) {
                return node.getElementsByTagName(tagName).length;
            })
        );
    }

    var rules = {};

    rules.paragraph = {
        filter: "p",

        replacement: function (content) {
            return "\n\n" + content + "\n\n";
        }
    };

    rules.lineBreak = {
        filter: "br",

        replacement: function (content, node, options) {
            return options.br + "\n";
        }
    };

    rules.heading = {
        filter: ["h1", "h2", "h3", "h4", "h5", "h6"],

        replacement: function (content, node, options) {
            var hLevel = Number(node.nodeName.charAt(1));

            if (options.headingStyle === "setext" && hLevel < 3) {
                var underline = repeat(
                    hLevel === 1 ? "=" : "-",
                    content.length
                );
                return "\n\n" + content + "\n" + underline + "\n\n";
            } else {
                return "\n\n" + repeat("#", hLevel) + " " + content + "\n\n";
            }
        }
    };

    rules.blockquote = {
        filter: "blockquote",

        replacement: function (content) {
            content = content.replace(/^\n+|\n+$/g, "");
            content = content.replace(/^/gm, "> ");
            return "\n\n" + content + "\n\n";
        }
    };

    rules.list = {
        filter: ["ul", "ol"],

        replacement: function (content, node) {
            var parent = node.parentNode;
            if (parent.nodeName === "LI" && parent.lastElementChild === node) {
                return "\n" + content;
            } else {
                return "\n\n" + content + "\n\n";
            }
        }
    };

    rules.listItem = {
        filter: "li",

        replacement: function (content, node, options) {
            content = content
                .replace(/^\n+/, "") // remove leading newlines
                .replace(/\n+$/, "\n") // replace trailing newlines with just a single one
                .replace(/\n/gm, "\n    "); // indent
            var prefix = options.bulletListMarker + "   ";
            var parent = node.parentNode;
            if (parent.nodeName === "OL") {
                var start = parent.getAttribute("start");
                var index = Array.prototype.indexOf.call(parent.children, node);
                prefix = (start ? Number(start) + index : index + 1) + ".  ";
            }
            return (
                prefix +
                content +
                (node.nextSibling && !/\n$/.test(content) ? "\n" : "")
            );
        }
    };

    rules.indentedCodeBlock = {
        filter: function (node, options) {
            return (
                options.codeBlockStyle === "indented" &&
                node.nodeName === "PRE" &&
                node.firstChild &&
                node.firstChild.nodeName === "CODE"
            );
        },

        replacement: function (content, node, options) {
            return (
                "\n\n    " +
                node.firstChild.textContent.replace(/\n/g, "\n    ") +
                "\n\n"
            );
        }
    };

    rules.fencedCodeBlock = {
        filter: function (node, options) {
            return (
                options.codeBlockStyle === "fenced" &&
                node.nodeName === "PRE" &&
                node.firstChild &&
                node.firstChild.nodeName === "CODE"
            );
        },

        replacement: function (content, node, options) {
            var className = node.firstChild.getAttribute("class") || "";
            var language = (className.match(/language-(\S+)/) || [null, ""])[1];
            var code = node.firstChild.textContent;

            var fenceChar = options.fence.charAt(0);
            var fenceSize = 3;
            var fenceInCodeRegex = new RegExp("^" + fenceChar + "{3,}", "gm");

            var match;
            while ((match = fenceInCodeRegex.exec(code))) {
                if (match[0].length >= fenceSize) {
                    fenceSize = match[0].length + 1;
                }
            }

            var fence = repeat(fenceChar, fenceSize);

            return (
                "\n\n" +
                fence +
                language +
                "\n" +
                code.replace(/\n$/, "") +
                "\n" +
                fence +
                "\n\n"
            );
        }
    };

    rules.horizontalRule = {
        filter: "hr",

        replacement: function (content, node, options) {
            return "\n\n" + options.hr + "\n\n";
        }
    };

    rules.inlineLink = {
        filter: function (node, options) {
            return (
                options.linkStyle === "inlined" &&
                node.nodeName === "A" &&
                node.getAttribute("href")
            );
        },

        replacement: function (content, node) {
            var href = node.getAttribute("href");
            var title = cleanAttribute(node.getAttribute("title"));
            if (title) title = ' "' + title + '"';
            return "[" + content + "](" + href + title + ")";
        }
    };

    rules.referenceLink = {
        filter: function (node, options) {
            return (
                options.linkStyle === "referenced" &&
                node.nodeName === "A" &&
                node.getAttribute("href")
            );
        },

        replacement: function (content, node, options) {
            var href = node.getAttribute("href");
            var title = cleanAttribute(node.getAttribute("title"));
            if (title) title = ' "' + title + '"';
            var replacement;
            var reference;

            switch (options.linkReferenceStyle) {
                case "collapsed":
                    replacement = "[" + content + "][]";
                    reference = "[" + content + "]: " + href + title;
                    break;
                case "shortcut":
                    replacement = "[" + content + "]";
                    reference = "[" + content + "]: " + href + title;
                    break;
                default:
                    var id = this.references.length + 1;
                    replacement = "[" + content + "][" + id + "]";
                    reference = "[" + id + "]: " + href + title;
            }

            this.references.push(reference);
            return replacement;
        },

        references: [],

        append: function (options) {
            var references = "";
            if (this.references.length) {
                references = "\n\n" + this.references.join("\n") + "\n\n";
                this.references = []; // Reset references
            }
            return references;
        }
    };

    rules.emphasis = {
        filter: ["em", "i"],

        replacement: function (content, node, options) {
            if (!content.trim()) return "";
            return options.emDelimiter + content + options.emDelimiter;
        }
    };

    rules.strong = {
        filter: ["strong", "b"],

        replacement: function (content, node, options) {
            if (!content.trim()) return "";
            return options.strongDelimiter + content + options.strongDelimiter;
        }
    };

    rules.code = {
        filter: function (node) {
            var hasSiblings = node.previousSibling || node.nextSibling;
            var isCodeBlock =
                node.parentNode.nodeName === "PRE" && !hasSiblings;

            return node.nodeName === "CODE" && !isCodeBlock;
        },

        replacement: function (content) {
            if (!content.trim()) return "";

            var delimiter = "`";
            var leadingSpace = "";
            var trailingSpace = "";
            var matches = content.match(/`+/gm);
            if (matches) {
                if (/^`/.test(content)) leadingSpace = " ";
                if (/`$/.test(content)) trailingSpace = " ";
                while (matches.indexOf(delimiter) !== -1)
                    delimiter = delimiter + "`";
            }

            return (
                delimiter + leadingSpace + content + trailingSpace + delimiter
            );
        }
    };

    rules.image = {
        filter: "img",

        replacement: function (content, node) {
            var alt = cleanAttribute(node.getAttribute("alt"));
            var src = node.getAttribute("src") || "";
            var title = cleanAttribute(node.getAttribute("title"));
            var titlePart = title ? ' "' + title + '"' : "";
            return src ? "![" + alt + "]" + "(" + src + titlePart + ")" : "";
        }
    };

    function cleanAttribute(attribute) {
        return attribute ? attribute.replace(/(\n+\s*)+/g, "\n") : "";
    }

    /**
     * Manages a collection of rules used to convert HTML to Markdown
     */

    function Rules(options) {
        this.options = options;
        this._keep = [];
        this._remove = [];

        this.blankRule = {
            replacement: options.blankReplacement
        };

        this.keepReplacement = options.keepReplacement;

        this.defaultRule = {
            replacement: options.defaultReplacement
        };

        this.array = [];
        for (var key in options.rules) this.array.push(options.rules[key]);
    }

    Rules.prototype = {
        add: function (key, rule) {
            this.array.unshift(rule);
        },

        keep: function (filter) {
            this._keep.unshift({
                filter: filter,
                replacement: this.keepReplacement
            });
        },

        remove: function (filter) {
            this._remove.unshift({
                filter: filter,
                replacement: function () {
                    return "";
                }
            });
        },

        forNode: function (node) {
            if (node.isBlank) return this.blankRule;
            var rule;

            if ((rule = findRule(this.array, node, this.options))) return rule;
            if ((rule = findRule(this._keep, node, this.options))) return rule;
            if ((rule = findRule(this._remove, node, this.options)))
                return rule;

            return this.defaultRule;
        },

        forEach: function (fn) {
            for (var i = 0; i < this.array.length; i++) fn(this.array[i], i);
        }
    };

    function findRule(rules, node, options) {
        for (var i = 0; i < rules.length; i++) {
            var rule = rules[i];
            if (filterValue(rule, node, options)) return rule;
        }
        return void 0;
    }

    function filterValue(rule, node, options) {
        var filter = rule.filter;
        if (typeof filter === "string") {
            if (filter === node.nodeName.toLowerCase()) return true;
        } else if (Array.isArray(filter)) {
            if (filter.indexOf(node.nodeName.toLowerCase()) > -1) return true;
        } else if (typeof filter === "function") {
            if (filter.call(rule, node, options)) return true;
        } else {
            throw new TypeError(
                "`filter` needs to be a string, array, or function"
            );
        }
    }

    /**
     * The collapseWhitespace function is adapted from collapse-whitespace
     * by Luc Thevenard.
     *
     * The MIT License (MIT)
     *
     * Copyright (c) 2014 Luc Thevenard <lucthevenard@gmail.com>
     *
     * Permission is hereby granted, free of charge, to any person obtaining a copy
     * of this software and associated documentation files (the "Software"), to deal
     * in the Software without restriction, including without limitation the rights
     * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
     * copies of the Software, and to permit persons to whom the Software is
     * furnished to do so, subject to the following conditions:
     *
     * The above copyright notice and this permission notice shall be included in
     * all copies or substantial portions of the Software.
     *
     * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
     * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
     * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
     * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
     * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
     * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
     * THE SOFTWARE.
     */

    /**
     * collapseWhitespace(options) removes extraneous whitespace from an the given element.
     *
     * @param {Object} options
     */
    function collapseWhitespace(options) {
        var element = options.element;
        var isBlock = options.isBlock;
        var isVoid = options.isVoid;
        var isPre =
            options.isPre ||
            function (node) {
                return node.nodeName === "PRE";
            };

        if (!element.firstChild || isPre(element)) return;

        var prevText = null;
        var prevVoid = false;

        var prev = null;
        var node = next(prev, element, isPre);

        while (node !== element) {
            if (node.nodeType === 3 || node.nodeType === 4) {
                // Node.TEXT_NODE or Node.CDATA_SECTION_NODE
                var text = node.data.replace(/[ \r\n\t]+/g, " ");

                if (
                    (!prevText || / $/.test(prevText.data)) &&
                    !prevVoid &&
                    text[0] === " "
                ) {
                    text = text.substr(1);
                }

                // `text` might be empty at this point.
                if (!text) {
                    node = remove(node);
                    continue;
                }

                node.data = text;

                prevText = node;
            } else if (node.nodeType === 1) {
                // Node.ELEMENT_NODE
                if (isBlock(node) || node.nodeName === "BR") {
                    if (prevText) {
                        prevText.data = prevText.data.replace(/ $/, "");
                    }

                    prevText = null;
                    prevVoid = false;
                } else if (isVoid(node)) {
                    // Avoid trimming space around non-block, non-BR void elements.
                    prevText = null;
                    prevVoid = true;
                }
            } else {
                node = remove(node);
                continue;
            }

            var nextNode = next(prev, node, isPre);
            prev = node;
            node = nextNode;
        }

        if (prevText) {
            prevText.data = prevText.data.replace(/ $/, "");
            if (!prevText.data) {
                remove(prevText);
            }
        }
    }

    /**
     * remove(node) removes the given node from the DOM and returns the
     * next node in the sequence.
     *
     * @param {Node} node
     * @return {Node} node
     */
    function remove(node) {
        var next = node.nextSibling || node.parentNode;

        node.parentNode.removeChild(node);

        return next;
    }

    /**
     * next(prev, current, isPre) returns the next node in the sequence, given the
     * current and previous nodes.
     *
     * @param {Node} prev
     * @param {Node} current
     * @param {Function} isPre
     * @return {Node}
     */
    function next(prev, current, isPre) {
        if ((prev && prev.parentNode === current) || isPre(current)) {
            return current.nextSibling || current.parentNode;
        }

        return current.firstChild || current.nextSibling || current.parentNode;
    }

    /*
     * Set up window for Node.js
     */

    var root = typeof window !== "undefined" ? window : {};

    /*
     * Parsing HTML strings
     */

    function canParseHTMLNatively() {
        var Parser = root.DOMParser;
        var canParse = false;

        // Adapted from https://gist.github.com/1129031
        // Firefox/Opera/IE throw errors on unsupported types
        try {
            // WebKit returns null on unsupported types
            if (new Parser().parseFromString("", "text/html")) {
                canParse = true;
            }
        } catch (e) {}

        return canParse;
    }

    function createHTMLParser() {
        var Parser = function () {};

        {
            if (shouldUseActiveX()) {
                Parser.prototype.parseFromString = function (string) {
                    var doc = new window.ActiveXObject("htmlfile");
                    doc.designMode = "on"; // disable on-page scripts
                    doc.open();
                    doc.write(string);
                    doc.close();
                    return doc;
                };
            } else {
                Parser.prototype.parseFromString = function (string) {
                    var doc = document.implementation.createHTMLDocument("");
                    doc.open();
                    doc.write(string);
                    doc.close();
                    return doc;
                };
            }
        }
        return Parser;
    }

    function shouldUseActiveX() {
        var useActiveX = false;
        try {
            document.implementation.createHTMLDocument("").open();
        } catch (e) {
            if (window.ActiveXObject) useActiveX = true;
        }
        return useActiveX;
    }

    var HTMLParser = canParseHTMLNatively()
        ? root.DOMParser
        : createHTMLParser();

    function RootNode(input) {
        var root;
        if (typeof input === "string") {
            var doc = htmlParser().parseFromString(
                // DOM parsers arrange elements in the <head> and <body>.
                // Wrapping in a custom element ensures elements are reliably arranged in
                // a single element.
                '<x-turndown id="turndown-root">' + input + "</x-turndown>",
                "text/html"
            );
            root = doc.getElementById("turndown-root");
        } else {
            root = input.cloneNode(true);
        }
        collapseWhitespace({
            element: root,
            isBlock: isBlock,
            isVoid: isVoid
        });

        return root;
    }

    var _htmlParser;
    function htmlParser() {
        _htmlParser = _htmlParser || new HTMLParser();
        return _htmlParser;
    }

    function Node(node) {
        node.isBlock = isBlock(node);
        node.isCode =
            node.nodeName.toLowerCase() === "code" || node.parentNode.isCode;
        node.isBlank = isBlank(node);
        node.flankingWhitespace = flankingWhitespace(node);
        return node;
    }

    function isBlank(node) {
        return (
            !isVoid(node) &&
            !isMeaningfulWhenBlank(node) &&
            /^\s*$/i.test(node.textContent) &&
            !hasVoid(node) &&
            !hasMeaningfulWhenBlank(node)
        );
    }

    function flankingWhitespace(node) {
        var leading = "";
        var trailing = "";

        if (!node.isBlock) {
            var hasLeading = /^\s/.test(node.textContent);
            var hasTrailing = /\s$/.test(node.textContent);
            var blankWithSpaces = node.isBlank && hasLeading && hasTrailing;

            if (hasLeading && !isFlankedByWhitespace("left", node)) {
                leading = " ";
            }

            if (
                !blankWithSpaces &&
                hasTrailing &&
                !isFlankedByWhitespace("right", node)
            ) {
                trailing = " ";
            }
        }

        return { leading: leading, trailing: trailing };
    }

    function isFlankedByWhitespace(side, node) {
        var sibling;
        var regExp;
        var isFlanked;

        if (side === "left") {
            sibling = node.previousSibling;
            regExp = / $/;
        } else {
            sibling = node.nextSibling;
            regExp = /^ /;
        }

        if (sibling) {
            if (sibling.nodeType === 3) {
                isFlanked = regExp.test(sibling.nodeValue);
            } else if (sibling.nodeType === 1 && !isBlock(sibling)) {
                isFlanked = regExp.test(sibling.textContent);
            }
        }
        return isFlanked;
    }

    var reduce = Array.prototype.reduce;
    var leadingNewLinesRegExp = /^\n*/;
    var trailingNewLinesRegExp = /\n*$/;
    var escapes = [
        [/\\/g, "\\\\"],
        [/\*/g, "\\*"],
        [/^-/g, "\\-"],
        [/^\+ /g, "\\+ "],
        [/^(=+)/g, "\\$1"],
        [/^(#{1,6}) /g, "\\$1 "],
        [/`/g, "\\`"],
        [/^~~~/g, "\\~~~"],
        [/\[/g, "\\["],
        [/\]/g, "\\]"],
        [/^>/g, "\\>"],
        [/_/g, "\\_"],
        [/^(\d+)\. /g, "$1\\. "]
    ];

    function TurndownService(options) {
        if (!(this instanceof TurndownService))
            return new TurndownService(options);

        var defaults = {
            rules: rules,
            headingStyle: "setext",
            hr: "* * *",
            bulletListMarker: "*",
            codeBlockStyle: "indented",
            fence: "```",
            emDelimiter: "_",
            strongDelimiter: "**",
            linkStyle: "inlined",
            linkReferenceStyle: "full",
            br: "  ",
            blankReplacement: function (content, node) {
                return node.isBlock ? "\n\n" : "";
            },
            keepReplacement: function (content, node) {
                return node.isBlock
                    ? "\n\n" + node.outerHTML + "\n\n"
                    : node.outerHTML;
            },
            defaultReplacement: function (content, node) {
                return node.isBlock ? "\n\n" + content + "\n\n" : content;
            }
        };
        this.options = extend({}, defaults, options);
        this.rules = new Rules(this.options);
    }

    TurndownService.prototype = {
        /**
         * The entry point for converting a string or DOM node to Markdown
         * @public
         * @param {String|HTMLElement} input The string or DOM node to convert
         * @returns A Markdown representation of the input
         * @type String
         */

        turndown: function (input) {
            if (!canConvert(input)) {
                throw new TypeError(
                    input +
                        " is not a string, or an element/document/fragment node."
                );
            }

            if (input === "") return "";

            var output = process.call(this, new RootNode(input));
            return postProcess.call(this, output);
        },

        /**
         * Add one or more plugins
         * @public
         * @param {Function|Array} plugin The plugin or array of plugins to add
         * @returns The Turndown instance for chaining
         * @type Object
         */

        use: function (plugin) {
            if (Array.isArray(plugin)) {
                for (var i = 0; i < plugin.length; i++) this.use(plugin[i]);
            } else if (typeof plugin === "function") {
                plugin(this);
            } else {
                throw new TypeError(
                    "plugin must be a Function or an Array of Functions"
                );
            }
            return this;
        },

        /**
         * Adds a rule
         * @public
         * @param {String} key The unique key of the rule
         * @param {Object} rule The rule
         * @returns The Turndown instance for chaining
         * @type Object
         */

        addRule: function (key, rule) {
            this.rules.add(key, rule);
            return this;
        },

        /**
         * Keep a node (as HTML) that matches the filter
         * @public
         * @param {String|Array|Function} filter The unique key of the rule
         * @returns The Turndown instance for chaining
         * @type Object
         */

        keep: function (filter) {
            this.rules.keep(filter);
            return this;
        },

        /**
         * Remove a node that matches the filter
         * @public
         * @param {String|Array|Function} filter The unique key of the rule
         * @returns The Turndown instance for chaining
         * @type Object
         */

        remove: function (filter) {
            this.rules.remove(filter);
            return this;
        },

        /**
         * Escapes Markdown syntax
         * @public
         * @param {String} string The string to escape
         * @returns A string with Markdown syntax escaped
         * @type String
         */

        escape: function (string) {
            return escapes.reduce(function (accumulator, escape) {
                return accumulator.replace(escape[0], escape[1]);
            }, string);
        }
    };

    /**
     * Reduces a DOM node down to its Markdown string equivalent
     * @private
     * @param {HTMLElement} parentNode The node to convert
     * @returns A Markdown representation of the node
     * @type String
     */

    function process(parentNode) {
        var self = this;
        return reduce.call(
            parentNode.childNodes,
            function (output, node) {
                node = new Node(node);

                var replacement = "";
                if (node.nodeType === 3) {
                    replacement = node.isCode
                        ? node.nodeValue
                        : self.escape(node.nodeValue);
                } else if (node.nodeType === 1) {
                    replacement = replacementForNode.call(self, node);
                }

                return join(output, replacement);
            },
            ""
        );
    }

    /**
     * Appends strings as each rule requires and trims the output
     * @private
     * @param {String} output The conversion output
     * @returns A trimmed version of the ouput
     * @type String
     */

    function postProcess(output) {
        var self = this;
        this.rules.forEach(function (rule) {
            if (typeof rule.append === "function") {
                output = join(output, rule.append(self.options));
            }
        });

        return output.replace(/^[\t\r\n]+/, "").replace(/[\t\r\n\s]+$/, "");
    }

    /**
     * Converts an element node to its Markdown equivalent
     * @private
     * @param {HTMLElement} node The node to convert
     * @returns A Markdown representation of the node
     * @type String
     */

    function replacementForNode(node) {
        var rule = this.rules.forNode(node);
        var content = process.call(this, node);
        var whitespace = node.flankingWhitespace;
        if (whitespace.leading || whitespace.trailing) content = content.trim();
        return (
            whitespace.leading +
            rule.replacement(content, node, this.options) +
            whitespace.trailing
        );
    }

    /**
     * Determines the new lines between the current output and the replacement
     * @private
     * @param {String} output The current conversion output
     * @param {String} replacement The string to append to the output
     * @returns The whitespace to separate the current output and the replacement
     * @type String
     */

    function separatingNewlines(output, replacement) {
        var newlines = [
            output.match(trailingNewLinesRegExp)[0],
            replacement.match(leadingNewLinesRegExp)[0]
        ].sort();
        var maxNewlines = newlines[newlines.length - 1];
        return maxNewlines.length < 2 ? maxNewlines : "\n\n";
    }

    function join(string1, string2) {
        var separator = separatingNewlines(string1, string2);

        // Remove trailing/leading newlines and replace with separator
        string1 = string1.replace(trailingNewLinesRegExp, "");
        string2 = string2.replace(leadingNewLinesRegExp, "");

        return string1 + separator + string2;
    }

    /**
     * Determines whether an input can be converted
     * @private
     * @param {String|HTMLElement} input Describe this parameter
     * @returns Describe what it returns
     * @type String|Object|Array|Boolean|Number
     */

    function canConvert(input) {
        return (
            input != null &&
            (typeof input === "string" ||
                (input.nodeType &&
                    (input.nodeType === 1 ||
                        input.nodeType === 9 ||
                        input.nodeType === 11)))
        );
    }

    return TurndownService;
})();