pretty-format 
Stringify any JavaScript value.
- Supports all built-in JavaScript types
 - Blazingly fast (similar performance to v8's 
JSON.stringifyand significantly faster than Node'sutil.format) - Plugin system for extending with custom types (i.e. 
ReactTestComponent) 
Installation
$ npm install pretty-format
Usage
var prettyFormat = require('pretty-format');
var obj = { property: {} };
obj.circularReference = obj;
obj[Symbol('foo')] = 'foo';
obj.map = new Map();
obj.map.set('prop', 'value');
obj.array = [1, NaN, Infinity];
console.log(prettyFormat(obj));
Result:
Object {
  "property": Object {},
  "circularReference": [Circular],
  "map": Map {
    "prop" => "value"
  },
  "array": Array [
    1,
    NaN,
    Infinity
  ],
  Symbol(foo): "foo"
}
Type Support
Object, Array, ArrayBuffer, DataView, Float32Array, Float64Array, Int8Array, Int16Array, Int32Array, Uint8Array, Uint8ClampedArray, Uint16Array, Uint32Array, arguments, Boolean, Date, Error, Function, Infinity, Map, NaN, null, Number, RegExp, Set, String, Symbol, undefined, WeakMap, WeakSet
Plugins
Pretty format also supports adding plugins:
var fooPlugin = {
  test: function(val) {
    return val && val.hasOwnProperty('foo');
  },
  print: function(val, print, indent) {
    return 'Foo: ' + print(val.foo);
  }
};
var obj = { foo: { bar: {} } };
prettyFormat(obj, {
  plugins: [fooPlugin]
});
// Foo: Object {
//   "bar": Object {}
// }
ReactTestComponent and ReactElement plugins
var prettyFormat = require('pretty-format');
var reactTestPlugin = require('pretty-format/plugins/ReactTestComponent');
var reactElementPlugin = require('pretty-format/plugins/ReactElement');
var React = require('react');
var renderer = require('react/lib/ReactTestRenderer');
var jsx = React.createElement('h1', null, 'Hello World');
prettyFormat(renderer.create(jsx).toJSON(), {
  plugins: [reactTestPlugin, reactElementPlugin]
});
// <h1>
//   Hello World
// </h1>