Difference between res.send and res.json in Express.js

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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.

The method also uses the json replacer and json spaces application settings, so you can format JSON with more options. Those options are set like so:

app.set('json spaces', 2);
app.set('json replacer', replacer);

And passed to a JSON.stringify() like so:

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 res.send() method doesn’t have:

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:

this.charset = this.charset || 'utf-8';
this.get('Content-Type') || this.set('Content-Type', 'application/json');

return this.send(body);

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