mithril-vndb/docs/jsonp.md

jsonp(options)

• API
• How it works
• Typical usage

---

API

stream = m.jsonp(options)

Argument	Type	Required	Description
options.url	String	Yes	The URL to send the request to. The URL may be either absolute or relative, and it may contain interpolations.
options.data	any	No	The data to be interpolated into the URL and serialized into the querystring (for GET requests) or body (for other types of requests).
options.type	any = Function(any)	No	A constructor to be applied to each object in the response. Defaults to the identity function.
options.initialValue	any	No	A value to populate the returned stream before the request completes
options.callbackName	String	No	The name of the function that will be called as the callback. Defaults to a randomized string (e.g. _mithril_6888197422121285_0({a: 1})
options.callbackKey	String	No	The name of the querystring parameter name that specifies the callback name. Defaults to callback (e.g. /someapi?callback=_mithril_6888197422121285_0)
returns	Stream		A stream that resolves to the response data, after it has been piped through type method

How to read signatures

---

How it works

The m.jsonp utility is useful for third party APIs that can return data in JSON-P format.

In a nutshell, JSON-P consists of creating a script tag whose src attribute points to a script that lives in the server outside of your control. Typically, you are required to define a global function and specify its name in the querystring of the script's URL. The response will return code that calls your global function, passing the server's data as the first parameter.

JSON-P has several limitations: it can only use GET requests, it implicitly trusts that the third party server won't serve malicious code and it requires polluting the global Javascript scope. Nonetheless, it is sometimes the only available way to retrieve data from a service (for example, if the service doesn't support CORS).

---

Typical usage

Some services follow the de-facto convention of responding with JSON-P if a callback querystring key is provided, thus making m.jsonp automatically work without any effort:

m.jsonp({url: "https://api.github.com/users/lhorie"}).run(function(response) {
	console.log(response.data.login) // logs "lhorie"
})

Some services do not follow conventions and therefore you must specify the callback key that the service expects:

m.jsonp({
	url: "https://api.flickr.com/services/feeds/photos_public.gne?tags=kitten&format=json",
	callbackKey: "jsoncallback",
})
.run(function(response) {
	console.log(response.link) // logs "https://www.flickr.com/photos/tags/kitten/"
})

And sometimes, you just want to take advantage of HTTP caching for GET requests for rarely-modified data:

//this request is always called with the same querystring, and therefore it is cached
m.jsonp({
	url: "https://api.github.com/users/lhorie"
	callbackName: "__callback"
})
.run(function(response) {
	console.log(response.data.login) // logs "lhorie"
})