pretty-print JSON using JavaScript

Question

How can I display JSON in an easy-to-read (for human readers) format? I\'m looking primarily for indentation and whitespace, with perhaps even colors / font-styles / etc.

Answer 1

var jsonObj = {"streetLabel": "Avenue Anatole France", "city": "Paris 07",  "postalCode": "75007", "countryCode": "FRA",  "countryLabel": "France" };

document.getElementById("result-before").innerHTML = JSON.stringify(jsonObj);

In case of displaying in HTML, you should to add a balise <pre></pre>

document.getElementById("result-after").innerHTML = "<pre>"+JSON.stringify(jsonObj,undefined, 2) +"</pre>"

Example:

var jsonObj = {"streetLabel": "Avenue Anatole France", "city": "Paris 07",  "postalCode": "75007", "countryCode": "FRA",  "countryLabel": "France" };

document.getElementById("result-before").innerHTML = JSON.stringify(jsonObj);

document.getElementById("result-after").innerHTML = "<pre>"+JSON.stringify(jsonObj,undefined, 2) +"</pre>"

div { float:left; clear:both; margin: 1em 0; }

<div id="result-before"></div>
<div id="result-after"></div>

Answer 2

Pretty-printing is implemented natively in JSON.stringify(). The third argument enables pretty printing and sets the spacing to use:

var str = JSON.stringify(obj, null, 2); // spacing level = 2

If you need syntax highlighting, you might use some regex magic like so:

function syntaxHighlight(json) {
    if (typeof json != 'string') {
         json = JSON.stringify(json, undefined, 2);
    }
    json = json.replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;');
    return json.replace(/("(\\u[a-zA-Z0-9]{4}|\\[^u]|[^\\"])*"(\s*:)?|\b(true|false|null)\b|-?\d+(?:\.\d*)?(?:[eE][+\-]?\d+)?)/g, function (match) {
        var cls = 'number';
        if (/^"/.test(match)) {
            if (/:$/.test(match)) {
                cls = 'key';
            } else {
                cls = 'string';
            }
        } else if (/true|false/.test(match)) {
            cls = 'boolean';
        } else if (/null/.test(match)) {
            cls = 'null';
        }
        return '<span class="' + cls + '">' + match + '</span>';
    });
}

See in action here: jsfiddle

Or a full snippet provided below:

function output(inp) {
    document.body.appendChild(document.createElement('pre')).innerHTML = inp;
}

function syntaxHighlight(json) {
    json = json.replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;');
    return json.replace(/("(\\u[a-zA-Z0-9]{4}|\\[^u]|[^\\"])*"(\s*:)?|\b(true|false|null)\b|-?\d+(?:\.\d*)?(?:[eE][+\-]?\d+)?)/g, function (match) {
        var cls = 'number';
        if (/^"/.test(match)) {
            if (/:$/.test(match)) {
                cls = 'key';
            } else {
                cls = 'string';
            }
        } else if (/true|false/.test(match)) {
            cls = 'boolean';
        } else if (/null/.test(match)) {
            cls = 'null';
        }
        return '<span class="' + cls + '">' + match + '</span>';
    });
}

var obj = {a:1, 'b':'foo', c:[false,'false',null, 'null', {d:{e:1.3e5,f:'1.3e5'}}]};
var str = JSON.stringify(obj, undefined, 4);

output(str);
output(syntaxHighlight(str));

pre {outline: 1px solid #ccc; padding: 5px; margin: 5px; }
.string { color: green; }
.number { color: darkorange; }
.boolean { color: blue; }
.null { color: magenta; }
.key { color: red; }

Answer 3

Here's user123444555621's awesome HTML one adapted for terminals. Handy for debugging Node scripts:

function prettyJ(json) {
  if (typeof json !== 'string') {
    json = JSON.stringify(json, undefined, 2);
  }
  return json.replace(/("(\\u[a-zA-Z0-9]{4}|\\[^u]|[^\\"])*"(\s*:)?|\b(true|false|null)\b|-?\d+(?:\.\d*)?(?:[eE][+\-]?\d+)?)/g, 
    function (match) {
      let cls = "\x1b[36m";
      if (/^"/.test(match)) {
        if (/:$/.test(match)) {
          cls = "\x1b[34m";
        } else {
          cls = "\x1b[32m";
        }
      } else if (/true|false/.test(match)) {
        cls = "\x1b[35m"; 
      } else if (/null/.test(match)) {
        cls = "\x1b[31m";
      }
      return cls + match + "\x1b[0m";
    }
  );
}

Usage:

// thing = any json OR string of json
prettyJ(thing);

Answer 4

User Pumbaa80's answer is great if you have an object you want pretty printed. If you're starting from a valid JSON string that you want to pretty printed, you need to convert it to an object first:

var jsonString = '{"some":"json"}';
var jsonPretty = JSON.stringify(JSON.parse(jsonString),null,2);  

This builds a JSON object from the string, and then converts it back to a string using JSON stringify's pretty print.

Answer 5

Thanks a lot @all! Based on the previous answers, here is another variant method providing custom replacement rules as parameter:

 renderJSON : function(json, rr, code, pre){
   if (typeof json !== 'string') {
      json = JSON.stringify(json, undefined, '\t');
   }
  var rules = {
   def : 'color:black;',    
   defKey : function(match){
             return '<strong>' + match + '</strong>';
          },
   types : [
       {
          name : 'True',
          regex : /true/,
          type : 'boolean',
          style : 'color:lightgreen;'
       },

       {
          name : 'False',
          regex : /false/,
          type : 'boolean',
          style : 'color:lightred;'
       },

       {
          name : 'Unicode',
          regex : /"(\\u[a-zA-Z0-9]{4}|\\[^u]|[^\\"])*"(\s*:)?/,
          type : 'string',
          style : 'color:green;'
       },

       {
          name : 'Null',
          regex : /null/,
          type : 'nil',
          style : 'color:magenta;'
       },

       {
          name : 'Number',
          regex : /-?\d+(?:\.\d*)?(?:[eE][+\-]?\d+)?/,
          type : 'number',
          style : 'color:darkorange;'
       },

       {
          name : 'Whitespace',
          regex : /\s+/,
          type : 'whitespace',
          style : function(match){
             return '&nbsp';
          }
       } 

    ],

    keys : [
       {
           name : 'Testkey',
           regex : /("testkey")/,
           type : 'key',
           style : function(match){
             return '<h1>' + match + '</h1>';
          }
       }
    ],

    punctuation : {
          name : 'Punctuation',
          regex : /([\,\.\}\{\[\]])/,
          type : 'punctuation',
          style : function(match){
             return '<p>________</p>';
          }
       }

  };

  if('undefined' !== typeof jQuery){
     rules = $.extend(rules, ('object' === typeof rr) ? rr : {});  
  }else{
     for(var k in rr ){
        rules[k] = rr[k];
     }
  }
    var str = json.replace(/([\,\.\}\{\[\]]|"(\\u[a-zA-Z0-9]{4}|\\[^u]|[^\\"])*"(\s*:)?|\b(true|false|null)\b|-?\d+(?:\.\d*)?(?:[eE][+\-]?\d+)?)/g, function (match) {
    var i = 0, p;
    if (rules.punctuation.regex.test(match)) {
               if('string' === typeof rules.punctuation.style){
                   return '<span style="'+ rules.punctuation.style + '">' + match + '</span>';
               }else if('function' === typeof rules.punctuation.style){
                   return rules.punctuation.style(match);
               } else{
                  return match;
               }            
    }

    if (/^"/.test(match)) {
        if (/:$/.test(match)) {
            for(i=0;i<rules.keys.length;i++){
            p = rules.keys[i];
            if (p.regex.test(match)) {
               if('string' === typeof p.style){
                   return '<span style="'+ p.style + '">' + match + '</span>';
               }else if('function' === typeof p.style){
                   return p.style(match);
               } else{
                  return match;
               }                
             }              
           }   
            return ('function'===typeof rules.defKey) ? rules.defKey(match) : '<span style="'+ rules.defKey + '">' + match + '</span>';            
        } else {
            return ('function'===typeof rules.def) ? rules.def(match) : '<span style="'+ rules.def + '">' + match + '</span>';
        }
    } else {
        for(i=0;i<rules.types.length;i++){
         p = rules.types[i];
         if (p.regex.test(match)) {
               if('string' === typeof p.style){
                   return '<span style="'+ p.style + '">' + match + '</span>';
               }else if('function' === typeof p.style){
                   return p.style(match);
               } else{
                  return match;
               }                
          }             
        }

     }

    });

  if(true === pre)str = '<pre>' + str + '</pre>';
  if(true === code)str = '<code>' + str + '</code>';
  return str;
 }

Answer 6

If you need this to work in a textarea the accepted solution will not work.

<textarea id='textarea'></textarea>

$("#textarea").append(formatJSON(JSON.stringify(jsonobject),true));

function formatJSON(json,textarea) {
    var nl;
    if(textarea) {
        nl = "
";
    } else {
        nl = "<br>";
    }
    var tab = "&#160;&#160;&#160;&#160;";
    var ret = "";
    var numquotes = 0;
    var betweenquotes = false;
    var firstquote = false;
    for (var i = 0; i < json.length; i++) {
        var c = json[i];
        if(c == '"') {
            numquotes ++;
            if((numquotes + 2) % 2 == 1) {
                betweenquotes = true;
            } else {
                betweenquotes = false;
            }
            if((numquotes + 3) % 4 == 0) {
                firstquote = true;
            } else {
                firstquote = false;
            }
        }

        if(c == '[' && !betweenquotes) {
            ret += c;
            ret += nl;
            continue;
        }
        if(c == '{' && !betweenquotes) {
            ret += tab;
            ret += c;
            ret += nl;
            continue;
        }
        if(c == '"' && firstquote) {
            ret += tab + tab;
            ret += c;
            continue;
        } else if (c == '"' && !firstquote) {
            ret += c;
            continue;
        }
        if(c == ',' && !betweenquotes) {
            ret += c;
            ret += nl;
            continue;
        }
        if(c == '}' && !betweenquotes) {
            ret += nl;
            ret += tab;
            ret += c;
            continue;
        }
        if(c == ']' && !betweenquotes) {
            ret += nl;
            ret += c;
            continue;
        }
        ret += c;
    } // i loop
    return ret;
}