The methods are identical when an object or array is passed, but res.json() will also convert non-objects, such as null and undefined , which are not valid JSON.(传递对象或数组时，方法是相同的，但res.json()也将转换非对象，例如null和undefined ，这些对象是无效的JSON。)
The method also uses the json replacer and json spaces application settings, so you can format JSON with more options.(该方法还使用json replacer和json spaces应用程序设置，因此您可以使用更多选项格式化JSON。) Those options are set like so:(这些选项设置如下：)
app.set('json spaces', 2);
app.set('json replacer', replacer);
And passed to a JSON.stringify() like so:(并传递给JSON.stringify()如下所示：)
JSON.stringify(value, replacer, spacing);
// value: object to format
// replacer: rules for transforming properties encountered during stringifying
// spacing: the number of spaces for indentation
This is the code in the res.json() method that the send method doesn't have:(这是send方法没有的res.json()方法中的代码：)
var app = this.app;
var replacer = app.get('json replacer');
var spaces = app.get('json spaces');
var body = JSON.stringify(obj, replacer, spaces);
The method ends up as a res.send() in the end:(该方法最终以res.send()结尾：)
this.charset = this.charset || 'utf-8';
this.get('Content-Type') || this.set('Content-Type', 'application/json');
return this.send(body);
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