Avert stringify result when result is string yet

[cpm828]

When I use jsonp request, if api response result as below

callback('{"timestamp": 1499421237, "nonceStr": "kAi5na4ckNG3uv3xg9MVdP"}');

We must use JSON.parse twice, so I think it's necessary to add a judge with body = typeof result === 'string' ? result : JSON.stringify(result)

What do you think！