Pretty printing XML with javascript

I have a string that represents a non indented XML that I would like to pretty-print. For example:

<root><node/></root>

should become:

<root>
  <node/>
</root>

Syntax highlighting is not a requirement. To tackle the problem I first transform the XML to add carriage returns and white spaces and then use a pre tag to output the XML. To add new lines and white spaces I wrote the following function:

function formatXml(xml) {
    var formatted = '';
    var reg = /(>)(<)(/*)/g;
    xml = xml.replace(reg, '$1rn$2$3');
    var pad = 0;
    jQuery.each(xml.split('rn'), function(index, node) {
        var indent = 0;
        if (node.match( /.+</w[^>]*>$/ )) {
            indent = 0;
        } else if (node.match( /^</w/ )) {
            if (pad != 0) {
                pad -= 1;
            }
        } else if (node.match( /^<w[^>]*[^/]>.*$/ )) {
            indent = 1;
        } else {
            indent = 0;
        }

        var padding = '';
        for (var i = 0; i < pad; i++) {
            padding += '  ';
        }

        formatted += padding + node + 'rn';
        pad += indent;
    });

    return formatted;
}

I then call the function like this:

jQuery('pre.formatted-xml').text(formatXml('<root><node1/></root>'));

This works perfectly fine for me but while I was writing the previous function I thought that there must be a better way. So my question is do you know of any better way given an XML string to pretty-print it in an html page? Any javascript frameworks and/or plugins that could do the job are welcome. My only requirement is this to be done on the client side.

From the text of the question I get the impression that a string result is expected, as opposed to an HTML-formatted result.

If this is so, the simplest way to achieve this is to process the XML document with the identity transformation and with an <xsl:output indent="yes"/> instruction:

<xsl:stylesheet version="1.0"
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
 <xsl:output omit-xml-declaration="yes" indent="yes"/>

    <xsl:template match="node()|@*">
      <xsl:copy>
        <xsl:apply-templates select="node()|@*"/>
      </xsl:copy>
    </xsl:template>
</xsl:stylesheet>

When applying this transformation on the provided XML document:

<root><node/></root>

most XSLT processors (.NET XslCompiledTransform, Saxon 6.5.4 and Saxon 9.0.0.2, AltovaXML) produce the wanted result:

<root>
  <node />
</root>

This can be done using native javascript tools, without 3rd party libs, extending the @Dimitre Novatchev’s answer:

var prettifyXml = function(sourceXml)
{
    var xmlDoc = new DOMParser().parseFromString(sourceXml, 'application/xml');
    var xsltDoc = new DOMParser().parseFromString([
        // describes how we want to modify the XML - indent everything
        '<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform">',
        '  <xsl:strip-space elements="*"/>',
        '  <xsl:template match="para[content-style][not(text())]">', // change to just text() to strip space in text nodes
        '    <xsl:value-of select="normalize-space(.)"/>',
        '  </xsl:template>',
        '  <xsl:template match="node()|@*">',
        '    <xsl:copy><xsl:apply-templates select="node()|@*"/></xsl:copy>',
        '  </xsl:template>',
        '  <xsl:output indent="yes"/>',
        '</xsl:stylesheet>',
    ].join('n'), 'application/xml');

    var xsltProcessor = new XSLTProcessor();    
    xsltProcessor.importStylesheet(xsltDoc);
    var resultDoc = xsltProcessor.transformToDocument(xmlDoc);
    var resultXml = new XMLSerializer().serializeToString(resultDoc);
    return resultXml;
};

console.log(prettifyXml('<root><node/></root>'));

Outputs:

<root>
  <node/>
</root>

JSFiddle

Note, as pointed out by @jat255, pretty printing with <xsl:output indent="yes"/> is not supported by firefox. It only seems to work in chrome, opera and probably the rest webkit-based browsers.

Slight modification of efnx clckclcks’s javascript function. I changed the formatting from spaces to tab, but most importantly I allowed text to remain on one line:

var formatXml = this.formatXml = function (xml) {
        var reg = /(>)s*(<)(/*)/g; // updated Mar 30, 2015
        var wsexp = / *(.*) +n/g;
        var contexp = /(<.+>)(.+n)/g;
        xml = xml.replace(reg, '$1n$2$3').replace(wsexp, '$1n').replace(contexp, '$1n$2');
        var pad = 0;
        var formatted = '';
        var lines = xml.split('n');
        var indent = 0;
        var lastType="other";
        // 4 types of tags - single, closing, opening, other (text, doctype, comment) - 4*4 = 16 transitions 
        var transitions = {
            'single->single': 0,
            'single->closing': -1,
            'single->opening': 0,
            'single->other': 0,
            'closing->single': 0,
            'closing->closing': -1,
            'closing->opening': 0,
            'closing->other': 0,
            'opening->single': 1,
            'opening->closing': 0,
            'opening->opening': 1,
            'opening->other': 1,
            'other->single': 0,
            'other->closing': -1,
            'other->opening': 0,
            'other->other': 0
        };

        for (var i = 0; i < lines.length; i++) {
            var ln = lines[i];

            // Luca Viggiani 2017-07-03: handle optional <?xml ... ?> declaration
            if (ln.match(/s*<?xml/)) {
                formatted += ln + "n";
                continue;
            }
            // ---

            var single = Boolean(ln.match(/<.+/>/)); // is this line a single tag? ex. <br />
            var closing = Boolean(ln.match(/</.+>/)); // is this a closing tag? ex. </a>
            var opening = Boolean(ln.match(/<[^!].*>/)); // is this even a tag (that's not <!something>)
            var type = single ? 'single' : closing ? 'closing' : opening ? 'opening' : 'other';
            var fromTo = lastType + '->' + type;
            lastType = type;
            var padding = '';

            indent += transitions[fromTo];
            for (var j = 0; j < indent; j++) {
                padding += 't';
            }
            if (fromTo == 'opening->closing')
                formatted = formatted.substr(0, formatted.length - 1) + ln + 'n'; // substr removes line break (n) from prev loop
            else
                formatted += padding + ln + 'n';
        }

        return formatted;
    };

Found this thread when I had a similar requirement but I simplified OP’s code as follows:

function formatXml(xml, tab) { // tab = optional indent value, default is tab (t)
    var formatted = '', indent="";
    tab = tab || 't';
    xml.split(/>s*</).forEach(function(node) {
        if (node.match( /^/w/ )) indent = indent.substring(tab.length); // decrease indent by one 'tab'
        formatted += indent + '<' + node + '>rn';
        if (node.match( /^<?w[^>]*[^/]$/ )) indent += tab;              // increase indent
    });
    return formatted.substring(1, formatted.length-3);
}

works for me!

Personnaly, I use google-code-prettify with this function :

prettyPrintOne('<root><node1><root>', 'xml')

Or if you’d just like another js function to do it, I’ve modified Darin’s (a lot):

var formatXml = this.formatXml = function (xml) {
    var reg = /(>)(<)(/*)/g;
    var wsexp = / *(.*) +n/g;
    var contexp = /(<.+>)(.+n)/g;
    xml = xml.replace(reg, '$1n$2$3').replace(wsexp, '$1n').replace(contexp, '$1n$2');
    var pad = 0;
    var formatted = '';
    var lines = xml.split('n');
    var indent = 0;
    var lastType="other";
    // 4 types of tags - single, closing, opening, other (text, doctype, comment) - 4*4 = 16 transitions 
    var transitions = {
        'single->single'    : 0,
        'single->closing'   : -1,
        'single->opening'   : 0,
        'single->other'     : 0,
        'closing->single'   : 0,
        'closing->closing'  : -1,
        'closing->opening'  : 0,
        'closing->other'    : 0,
        'opening->single'   : 1,
        'opening->closing'  : 0, 
        'opening->opening'  : 1,
        'opening->other'    : 1,
        'other->single'     : 0,
        'other->closing'    : -1,
        'other->opening'    : 0,
        'other->other'      : 0
    };

    for (var i=0; i < lines.length; i++) {
        var ln = lines[i];
        var single = Boolean(ln.match(/<.+/>/)); // is this line a single tag? ex. <br />
        var closing = Boolean(ln.match(/</.+>/)); // is this a closing tag? ex. </a>
        var opening = Boolean(ln.match(/<[^!].*>/)); // is this even a tag (that's not <!something>)
        var type = single ? 'single' : closing ? 'closing' : opening ? 'opening' : 'other';
        var fromTo = lastType + '->' + type;
        lastType = type;
        var padding = '';

        indent += transitions[fromTo];
        for (var j = 0; j < indent; j++) {
            padding += '    ';
        }

        formatted += padding + ln + 'n';
    }

    return formatted;
};

All of the javascript functions given here won’t work for an xml document having unspecified white spaces between the end tag ‘>’ and the start tag ‘<‘. To fix them, you just need to replace the first line in the functions

var reg = /(>)(<)(/*)/g;

by

var reg = /(>)s*(<)(/*)/g;

what about creating a stub node (document.createElement(‘div’) – or using your library equivalent), filling it with the xml string (via innerHTML) and calling simple recursive function for the root element/or the stub element in case you don’t have a root. The function would call itself for all the child nodes.

You could then syntax-highlight along the way, be certain the markup is well-formed (done automatically by browser when appending via innerHTML) etc. It wouldn’t be that much code and probably fast enough.

If you are looking for a JavaScript solution just take the code from the Pretty Diff tool at http://prettydiff.com/?m=beautify

You can also send files to the tool using the s parameter, such as:
http://prettydiff.com/?m=beautify&s=https://stackoverflow.com/

Or just print out the special HTML characters?

Ex: <xmlstuff>&#10; &#09;<node />&#10;</xmlstuff>   


&#09;   Horizontal tab  
&#10;   Line feed

XMLSpectrum formats XML, supports attribute indentation and also does syntax-highlighting for XML and any embedded XPath expressions:

XMLSpectrum formatted XML

XMLSpectrum is an open source project, coded in XSLT 2.0 – so you can run this server-side with a processor such as Saxon-HE (recommended) or client-side using Saxon-CE.

XMLSpectrum is not yet optimised to run in the browser – hence the recommendation to run this server-side.

here is another function to format xml

function formatXml(xml){
    var out = "";
    var tab = "    ";
    var indent = 0;
    var inClosingTag=false;
    var dent=function(no){
        out += "n";
        for(var i=0; i < no; i++)
            out+=tab;
    }


    for (var i=0; i < xml.length; i++) {
        var c = xml.charAt(i);
        if(c=='<'){
            // handle </
            if(xml.charAt(i+1) == "https://stackoverflow.com/"){
                inClosingTag = true;
                dent(--indent);
            }
            out+=c;
        }else if(c=='>'){
            out+=c;
            // handle />
            if(xml.charAt(i-1) == "https://stackoverflow.com/"){
                out+="n";
                //dent(--indent)
            }else{
              if(!inClosingTag)
                dent(++indent);
              else{
                out+="n";
                inClosingTag=false;
              }
            }
        }else{
          out+=c;
        }
    }
    return out;
}

You can get pretty formatted xml with xml-beautify

var prettyXmlText = new XmlBeautify().beautify(xmlText, 
                    {indent: "  ",useSelfClosingElement: true});

indent:indent pattern like white spaces

useSelfClosingElement: true=>use self-closing element when empty element.

JSFiddle

Original(Before)

<?xml version="1.0" encoding="utf-8"?><example version="2.0">
  <head><title>Original aTitle</title></head>
  <body info="none" ></body>
</example>

Beautified(After)

<?xml version="1.0" encoding="utf-8"?>
<example version="2.0">
  <head>
    <title>Original aTitle</title>
  </head>
  <body info="none" />
</example>

For a current project I had the need to prettify and colorize XML without extra libraries. The following self contained code works quite well.

function formatXml(xml,colorize,indent) { 
  function esc(s){return s.replace(/[-/&<> ]/g,function(c){          // Escape special chars
    return c==' '?'&nbsp;':'&#'+c.charCodeAt(0)+';';});}            
  var sm='<div id="xmt">',se="<div id="xel">",sd='<div id="xdt">',
      sa="<div id="xat">",tb='<div id="xtb">',tc="<div id="xtc">",
      id=indent||'  ',sz=tz='</div>',re=is="",ib,ob,at,i;
  if (!colorize) sm=se=sd=sa=sz='';   
  xml.slice(1,-1).split(/>s*</).forEach(function(nd){
    ob=('<'+nd+'>').match(/^(<[!?/]?)(.*?)([?/]?>)$/);              // Split outer brackets
    ib=ob[2].match(/^(.*?)>(.*)</(.*)$/)||['',ob[2],''];             // Split inner brackets 
    at=ib[1].match(/^--.*--$|=|('|").*?1|[^tnf />"'=]+/g)||['']; // Split attributes
    if (ob[1]=='</') is=is.substring(id.length);                      // Decrease indent
    re+=tb+tc+esc(is)+tz+tc+sm+esc(ob[1])+sz+se+esc(at[0])+sz;
    for (i=1;i<at.length;i++) re+=(at[i]=="="?sm+"="+sz+sd+esc(at[++i]):sa+' '+at[i])+sz;
    re+=ib[2]?sm+esc('>')+sz+sd+esc(ib[2])+sz+sm+esc('</')+sz+se+ib[3]+sz:'';
    re+=sm+esc(ob[3])+sz+tz+tz;
    if (ob[1]+ob[3]+ib[2]=='<>') is+=id;                              // Increase indent
  });
  return re;
}

See https://jsfiddle.net/3n0cazL8/

var formatXml = this.formatXml = function (xml) {
        var reg = /(>)(<)(/*)/g;
        var wsexp = / *(.*) +n/g;
        var contexp = /(<.+>)(.+n)/g;
        xml = xml.replace(reg, '$1n$2$3').replace(wsexp, '$1n').replace(contexp, '$1n$2');
        var pad = 0;
        var formatted = '';
        var lines = xml.split('n');
        var indent = 0;
        var lastType="other";

var reg = /(>)s*(<)(/*)/g;
xml = xml.replace(/r|n/g, ''); //deleting already existing whitespaces
xml = xml.replace(reg, '$1rn$2$3');

Use above method for pretty print and then add this in any div by using jquery text() method. for example id of div is xmldiv then use :

$("#xmldiv").text(formatXml(youXmlString));

You could also use Saxon-JS client-side:

<script src="SaxonJS/SaxonJS2.js"></script>

<script>
let myXML = `<root><node/></root>`;

SaxonJS.getResource({
   text: myXML.replace(`xml:space="preserve"`, ''),
   type: "xml"
}).then(doc => {
   const output = SaxonJS.serialize(doc, {method: "xml", indent: true, "omit-xml-declaration":true});
   console.log(output);
})
</script>

Saxon-JS Installation client-side
Saxon-JS Download page

Xml formatting can be done by parsing the xml, adding or changing text nodes in the dom tree for indentation and then serializing the DOM back to xml.

Please check formatxml function in https://jsonbrowser.sourceforge.io/formatxml.js
You can see the function in action in https://jsonbrowser.sourceforge.io/
under the Xml tab.

Below is the simplified code.
formatxml.js adds error checking, optional removal of comments, indent as a parameter and handles non-space text between parent nodes.

const parser = new DOMParser();

const serializer = new XMLSerializer();

function formatXml(xml) {
  let xmlDoc = parser.parseFromString(xml, 'application/xml');
  let rootElement = xmlDoc.documentElement;
  indentChildren(xmlDoc, rootElement, "n", "n  ");
  xml = serializer.serializeToString(xmlDoc);
  return xml;
}

function indentChildren(xmlDoc, node, prevPrefix, prefix) {
  let children = node.childNodes;
  let i;
  let prevChild = null;
  let prevChildType = 1;
  let child = null;
  let childType;
  for (i = 0; i < children.length; i++) {
    child = children[i];
    childType = child.nodeType;
    if (childType != 3) {
      if (prevChildType == 3) {
        // Update prev text node with correct indent
        prevChild.nodeValue = prefix;
      } else {
        // Create and insert text node with correct indent
        let textNode = xmlDoc.createTextNode(prefix);
        node.insertBefore(textNode, child);
        i++;
      }
      if (childType == 1) {
        let isLeaf = child.childNodes.length == 0 || child.childNodes.length == 1 && child.childNodes[0].nodeType != 1;
        if (!isLeaf) {
          indentChildren(xmlDoc, child, prefix, prefix + "  ");
        }
      }
    }
    prevChild = child;
    prevChildType =childType;
  }
  if (child != null) {
    // Previous level indentation after last child
    if (childType == 3) {
      child.nodeValue = prevPrefix;
    } else {
      let textNode = xmlDoc.createTextNode(prevPrefix);
      node.append(textNode);
    }
  }
}

Reference: https://www.w3schools.com/XML/dom_intro.asp

Xml-to-json library has method formatXml(xml). I am the maintainer of the project.

var prettyXml = formatXml("<a><b/></a>");

// <a>
//   <b/>
// </a>

This my version, maybe usefull for others, using String builder
Saw that someone had the same piece of code.

    public String FormatXml(String xml, String tab)
    {
        var sb = new StringBuilder();
        int indent = 0;
        // find all elements
        foreach (string node in Regex.Split(xml,@">s*<"))
        {
            // if at end, lower indent
            if (Regex.IsMatch(node, @"^/w")) indent--;
            sb.AppendLine(String.Format("{0}<{1}>", string.Concat(Enumerable.Repeat(tab, indent).ToArray()), node));
            // if at start, increase indent
            if (Regex.IsMatch(node, @"^<?w[^>]*[^/]$")) indent++;
        }
        // correct first < and last > from the output
        String result = sb.ToString().Substring(1);
        return result.Remove(result.Length - Environment.NewLine.Length-1);
    }

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