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, ‘&’).replace(//g, ‘>’);
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 ‘‘ + match + ‘‘;
});
}
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, ‘&’).replace(//g, ‘>’);
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 ‘‘ + match + ‘‘;
});
}
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; }
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.