yfetch

Yet another fetch. A guide for "How to make fetch more beautiful?".

fetch is a new API based on Promise, it help you to prevent callback hell.

I like fetch, so here is a set of use cases and example codes to know how to use yfetch or make your fetch coding style better.

Core Features:

• A set of transform functions to help you to deal with fetch request or response.
• support JSONP at client side.
• Accept same options just like fetch with some extensions:
  • opts.base : base url
  • opts.query : will be appended into url automatically
  • opts.url : pass into fetch() as 1st param with processed opts.base and opts.query
  • opts.json : auto json headers in request, then json parse the response.body
  • opts.ignoreJsonError : ignore JSON parse error, and the respose.body will be a string
  • opts.error : rejects when the response http code be included in opts.error array
  • response.body : auto resolved as String or JSON
  • response.parsed : true when opts.json successed
  • response.headers : auto transformed as Object from Header
  • response.fetchArgs : the arguments of the fetch call
• debug , export DEBUG=... to show debug log:
  • yfetch:start: show url and fetch arguments just before the request starts
  • yfetch:raw : show url, response size, status, headers, raw
  • yfetch:result : show url, response status, body as text or JSON
  • yfetch:error : show url, response status, body as text or JSON, error

Install

npm install yfetch --save

You will need these polyfills for older browsers or other environments:

• Promise : browser support
• fetch : browser support

Usage

import yfetch from 'yfetch';

// Same as fetch('https://some.where/test?page=10&size=5', {})
yfetch({
  url: '/test',
  base: 'https://some.where',
  query: {
    page: 10,
    size: 5
  }
}).then((ret) => console.log(ret));

/*
{
  url: 'https://some.where/test?page=10&size=5',
  headers: { ... },
  status: 200,
  statusText: 'OK',
  ok: true,
  body: '...',                                  // yfetch transformed text or JSON
  size: 1234,
  fetchArgs: [                                  // yfetch exntends attribute,
    'https://some.where/test?page=10&size=5',   // original fetch arguments stores here
    {}
  ]
}
*/

JSONP

You will need fetch-jsonp for JSONP feature. When you set { jsonp: true } in yfetch arguments and global.fetchJsonp() exists, the request will made by jsonp.

import yfetch from 'yfetch';

yfetch({
  url: 'http://another.host.com/jsonp',
  jsonp: true,                          // Required for jsonp
  // Allow fetch-jsonp options https://github.com/camsong/fetch-jsonp
  jsonpCallback: 'custom_callback_param_name',            // Optional
  jsonpCallbackFunction: 'custom_callback_function_name', // Optional
}).then((ret) => console.log(ret.body));

To ensure global.fetchJsonp() ready at client side, you can add these:

import fetchJsonp from 'fetch-jsonp'

if (global.window) {
  global.fetchJsonp = fetchJsonp
}

Why I need yfetch?

Check these daily use cases, you may use yfetch to make things simple, or just do the same task with more code.

Get Response body

fetch(url, opts)
.then((response) => response.body.text())
.then (body => {
    // body, but response dropped
});

yfetch({ url, ...opts })
.then(response => {
    // response.body
});

Get Response as JSON

fetch(url, { headers: { Accept: 'application/json' }, ...opts })
.then((response) => response.body.json())
.then (body => {
    // body as JSON, but response dropped
});

yfetch({ url, json: true, ...opts })
.then(response => {
    // response.body as JSON
});

Debug

// ES6 arrow function to return the promise
myfetch = (url, opts) => fetch(url, opts)
.then((response) => response.body.json())
.then (
body => console.log('success', body, url, opts),
error => console.log('error', error, url, opts)
);

// always use the wrapped version
myfetch(url, opts);

// debug in your code....deprecated
yfetch({ url, ...opts })
.then(
resp => console.log('success', resp.body, resp.fetchArgs),
error => console.log('error', error, error.fetchArgs)
);

// BETTER: export DEBUG=yfetch:* then
// just do yfetch without changing your code
yfetch({url, json: true, ...opts})

Conclusion

You always need a wrapped version of fetch for debugging and response handling, you can just use yfetch, or do it your own. If you do not use yfetch, we still encourage you to use ES6 coding style to make your fetch more beautiful. In simple words, yfetch is:

const yfetch = (opts = {}) => {
    const fetchArgs = transformFetchOptions(opts);
    return fetch(...fetchArgs)
    .then(transformForContext(fetchArgs))
    .then(transformFetchResult)
    .catch(transformFetchError(fetchArgs));
}

You can build your own transformFetchOptions, transformForContext, transformFetchResult and transformFetchError , or just enjoy yfetch and reuse the exported yfetch transform functions. Review yfetch source code , then make your decision.

Transform functions

transformFetchOptions(opts)

Deal with opts.base, opts.url and opts.query.

import { transformFetchOptions } from 'yfetch';

transformFetchOptions({}));     // ['', {}]
transformFetchOptions({ base: 'pre_' }));   // ['pre_', {}]
transformFetchOptions({ url: 'test' }));    // ['test', {}]
transformFetchOptions({ base: 'pre_', url: 'test' }));      // ['pre_test', {}]
transformFetchOptions({ url: 'test', query: { foo: 'bar' } }));      // ['test?foo=bar', {}]

transformFetchOptions({ url: 'ya', json: true }));
// ['ya', {
//   json: true,
//   headers: {
//     Accept: 'application/json',
//     'Content-Type': 'application/json' } }]

transformFetchResult(response)

The response must contains .fetchArgs property. Deal with opts.json and opts.error.

import { transformFetchResult } from 'yfetch';

transformFetchResult({body, fetchArgs: [url, {json: true}}]);       // will JSON.parse(body)
transformFetchResult({code: 404, fetchArgs: [url, {error: [404, 500]}}]);   // will throw