Purpose and use of 'jsonp callback' setting in module /config/lib/express.js

[miller-productions]

Hi everyone,

This is a similar question to #1447

A query regarding a setting in module config/lib/express.js...

Inside the function initMiddleware there is the following call:

app.enable('jsonp callback');

What is the intent behind this? By the looks of it, it is related to whether or not the app enables jsonp callback support, however I am puzzled as to how/where this is used. Is it deprecated? Or, perhaps, is the express API doc missing this? I ask this question for the following reasons:

1. this setting doesn't appear to be used/read anywhere else in the app. i.e. a search here in the github repository for the setting jsonp callback returns only a single result, i.e. where it is set. I understand from this that it is probably not intended to be 'used' by the app but rather by the express module internally;
2. according to the express API doc, app.enable(name) sets the Boolean setting name to true, where name is one of the properties from the app settings table. However, I note that jsonp callback isn't listed in said app settings table.

Thanks for your time reading and considering this question.

Sincerely,
Dan

[lirantal]

@danoz-direct thanks for bringing this up.
I don't think it's required anymore but the option does exist, if you look at the settings table you pointed (http://expressjs.com/en/4x/api.html#app.settings.table) then it's there with a default 'callback' handler if the name is not specified.

[mleanos]

Resolved with #1463