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

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

What is actual difference between res.send and res.json as both seems to perform same operation of responding to client.


Solution 1:

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 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);

Solution 2:


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res.json eventually calls res.send, but before that it:

  • respects the json spaces and json replacer app settings
  • ensures the response will have utf8 charset and application/json content-type

Solution 3:

Looking in the headers sent…
res.send uses content-type:text/html
res.json uses content-type:application/json