JSONP
JSON wearing a JavaScript costume.
Where it came from
JSONP ("JSON with Padding") was the workaround for the browser same-origin policy before CORS existed. A 〈script〉 tag can load anything cross-domain, so APIs wrapped JSON in a function call: callback(﹛"a":1﹜).
It powered early AJAX against third-party APIs (Twitter, Flickr). Once CORS arrived, JSONP became a security liability and faded — but legacy endpoints still serve it.
How it works
A JSONP response is not JSON: it is JavaScript of the form fn(〈json〉). The "padding" is the callback name. To use it you inject a 〈script〉 and define fn to catch the data.
Converting means stripping the wrapper to recover pure JSON, or re-wrapping JSON with a callback. UWC does both in the browser — handy when a stubborn old API only speaks JSONP.
Convert JSONP
Unwrap JSONP into clean JSON (or wrap it back) — instantly, on your machine.