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; }