ky

by sindresorhus

sindresorhus / ky

🌳 Tiny & elegant HTTP client based on window.fetch

5.9K Stars 207 Forks Last release: 22 days ago (v0.24.0) MIT License 177 Commits 33 Releases

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ky

Huge thanks to for sponsoring me!





Ky is a tiny and elegant HTTP client based on the browser Fetch API

Build Status codecov

Ky targets modern browsers and Deno. For older browsers, you will need to transpile and use a

fetch
polyfill. For Node.js, check out Got. For isomorphic needs (like SSR), check out
ky-universal
.

It's just a tiny file with no dependencies.

Benefits over plain
fetch

  • Simpler API
  • Method shortcuts (
    ky.post()
    )
  • Treats non-2xx status codes as errors (after redirects)
  • Retries failed requests
  • JSON option
  • Timeout support
  • URL prefix option
  • Instances with custom defaults
  • Hooks

Install

$ npm install ky
Download
CDN

Usage

import ky from 'ky';

(async () => { const parsed = await ky.post('https://example.com', {json: {foo: true}}).json();

console.log(parsed);
//=> `{data: '🦄'}`

})();

With plain

fetch
, it would be:
(async () => {
    class HTTPError extends Error {}

const response = await fetch('https://example.com', {
    method: 'POST',
    body: JSON.stringify({foo: true}),
    headers: {
        'content-type': 'application/json'
    }
});

if (!response.ok) {
    throw new HTTPError(`Fetch error: ${response.statusText}`);
}

const parsed = await response.json();

console.log(parsed);
//=> `{data: '🦄'}`

})();

If you are using Deno, import Ky from a URL. For example, using a CDN:

import ky from 'https://unpkg.com/ky/index.js';

In environments that do not support

import
, you can load
ky
in UMD format. For example, using
require()
:
const ky = require('ky/umd');

With the UMD version, it's also easy to use

ky
without a bundler or module system.

API

ky(input, options?)

The

input
and
options
are the same as
fetch
, with some exceptions:
  • The
    credentials
    option is
    same-origin
    by default, which is the default in the spec too, but not all browsers have caught up yet.
  • Adds some more options. See below.

Returns a

Response
object with
Body
methods
added for convenience. So you can, for example, call

ky.get(input).json()
directly without having to await the
Response
first. When called like that, an appropriate
Accept
header will be set depending on the body method used. Unlike the
Body
methods of
window.Fetch
; these will throw an
HTTPError
if the response status is not in the range of
200...299
. Also,
.json()
will return an empty string if the response status is
204
instead of throwing a parse error due to an empty body.

ky.get(input, options?)

ky.post(input, options?)

ky.put(input, options?)

ky.patch(input, options?)

ky.head(input, options?)

ky.delete(input, options?)

Sets

options.method
to the method name and makes a request.

When using a

Request
instance as
input
, any URL altering options (such as
prefixUrl
) will be ignored.

options

Type:

object
method

Type:

string
\ Default:
'get'

HTTP method used to make the request.

Internally, the standard methods (

GET
,
POST
,
PUT
,
PATCH
,
HEAD
and
DELETE
) are uppercased in order to avoid server errors due to case sensitivity.
json

Type:

object
and any other value accepted by
JSON.stringify()

Shortcut for sending JSON. Use this instead of the

body
option. Accepts any plain object or value, which will be
JSON.stringify()
'd and sent in the body with the correct header set.
searchParams

Type:

string | object | Array> | URLSearchParams
\ Default:
''

Search parameters to include in the request URL. Setting this will override all existing search parameters in the input URL.

Accepts any value supported by

URLSearchParams()
.

prefixUrl

Type:

string | URL

A prefix to prepend to the

input
URL when making the request. It can be any valid URL, either relative or absolute. A trailing slash
/
is optional and will be added automatically, if needed, when it is joined with
input
. Only takes effect when
input
is a string. The
input
argument cannot start with a slash
/
when using this option.

Useful when used with

ky.extend()
to create niche-specific Ky-instances.

import ky from 'ky';

// On https://example.com

(async () => { await ky('unicorn', {prefixUrl: '/api'}); //=> 'https://example.com/api/unicorn'

await ky('unicorn', {prefixUrl: 'https://cats.com'});
//=> 'https://cats.com/unicorn'

})();

Notes: - After

prefixUrl
and
input
are joined, the result is resolved against the base URL of the page (if any). - Leading slashes in
input
are disallowed when using this option to enforce consistency and avoid confusion about how the
input
URL is handled, given that
input
will not follow the normal URL resolution rules when
prefixUrl
is being used, which changes the meaning of a leading slash.
retry

Type:

object | number
\ Default: -
limit
:
2
-
methods
:
get
put
head
delete
options
trace
-
statusCodes
:
408
413
429
500
502
503
504
-
maxRetryAfter
:
undefined

An object representing

limit
,
methods
,
statusCodes
and
maxRetryAfter
fields for maximum retry count, allowed methods, allowed status codes and maximum
Retry-After
time.

If

retry
is a number, it will be used as
limit
and other defaults will remain in place.

If

maxRetryAfter
is set to
undefined
, it will use
options.timeout
. If
Retry-After
header is greater than
maxRetryAfter
, it will cancel the request.

Delays between retries is calculated with the function

0.3 * (2 ** (retry - 1)) * 1000
, where
retry
is the attempt number (starts from 1).
import ky from 'ky';

(async () => { const parsed = await ky('https://example.com', { retry: { limit: 10, methods: ['get'], statusCodes: [413] } }).json(); })();

timeout

Type:

number | false
\ Default:
10000

Timeout in milliseconds for getting a response. Can not be greater than 2147483647. If set to

false
, there will be no timeout.
hooks

Type:

object
\ Default:
{beforeRequest: [], beforeRetry: [], afterResponse: []}

Hooks allow modifications during the request lifecycle. Hook functions may be async and are run serially.

hooks.beforeRequest

Type:

Function[]
\ Default:
[]

This hook enables you to modify the request right before it is sent. Ky will make no further changes to the request after this. The hook function receives

request
and
options
as arguments. You could, for example, modify the
request.headers
here.

The hook can return a

Request
to replace the outgoing request, or return a
Response
to completely avoid making an HTTP request. This can be used to mock a request, check an internal cache, etc. An important consideration when returning a request or response from this hook is that any remaining

beforeRequest
hooks will be skipped, so you may want to only return them from the last hook.
import ky from 'ky';

const api = ky.extend({ hooks: { beforeRequest: [ request => { request.headers.set('X-Requested-With', 'ky'); } ] } });

(async () => { const users = await api.get('https://example.com/api/users'); // ... })();

hooks.beforeRetry

Type:

Function[]
\ Default:
[]

This hook enables you to modify the request right before retry. Ky will make no further changes to the request after this. The hook function receives an object with the normalized request and options, an error instance, and the retry count. You could, for example, modify

request.headers
here.

If the request received a response, it will be available at

error.response
. Be aware that some types of errors, such as network errors, inherently mean that a response was not received.
import ky from 'ky';

(async () => { await ky('https://example.com', { hooks: { beforeRetry: [ async ({request, options, error, retryCount}) => { const token = await ky('https://example.com/refresh-token'); request.headers.set('Authorization', token ${token}); } ] } }); })();

hooks.afterResponse

Type:

Function[]
\ Default:
[]

This hook enables you to read and optionally modify the response. The hook function receives normalized request, options, and a clone of the response as arguments. The return value of the hook function will be used by Ky as the response object if it's an instance of

Response
.

import ky from 'ky';

(async () => { await ky('https://example.com', { hooks: { afterResponse: [ (_request, _options, response) => { // You could do something with the response, for example, logging. log(response);

                // Or return a `Response` instance to overwrite the response.
                return new Response('A different response', {status: 200});
            },

            // Or retry with a fresh token on a 403 error
            async (request, options, response) => {
                if (response.status === 403) {
                    // Get a fresh token
                    const token = await ky('https://example.com/token').text();

                    // Retry with the token
                    request.headers.set('Authorization', `token ${token}`);

                    return ky(request);
                }
            }
        ]
    }
});

})();

throwHttpErrors

Type:

boolean
\ Default:
true

Throw an

HTTPError
when, after following redirects, the response has a non-2xx status code. To also throw for redirects instead of following them, set the
redirect
option to
'manual'
.

Setting this to

false
may be useful if you are checking for resource availability and are expecting error responses.
onDownloadProgress

Type:

Function

Download progress event handler.

The function receives a

progress
and
chunk
argument: - The
progress
object contains the following elements:
percent
,
transferredBytes
and
totalBytes
. If it's not possible to retrieve the body size,
totalBytes
will be
0
. - The
chunk
argument is an instance of
Uint8Array
. It's empty for the first call.
import ky from 'ky';

(async () => { await ky('https://example.com', { onDownloadProgress: (progress, chunk) => { // Example output: // 0% - 0 of 1271 bytes // 100% - 1271 of 1271 bytes console.log(${progress.percent * 100}% - ${progress.transferredBytes} of ${progress.totalBytes} bytes); } }); })();

parseJson

Type:

Function
\ Default:
JSON.parse()

User-defined JSON-parsing function.

Use-cases: 1. Parse JSON via the

bourne
package to protect from prototype pollution. 2. Parse JSON with
reviver
option of
JSON.parse()
.

import ky from 'ky';
import bourne from '@hapijs/bourne';

(async () => { const parsed = await ky('https://example.com', { parseJson: text => bourne(text) }).json(); })();

fetch

Type:

Function
\ Default:
fetch

User-defined

fetch
function. Has to be fully compatible with the Fetch API standard.

Use-cases: 1. Use custom

fetch
implementations like
isomorphic-unfetch
. 2. Use the
fetch
wrapper function provided by some frameworks that use server-side rendering (SSR).
import ky from 'ky';
import fetch from 'isomorphic-unfetch';

(async () => { const parsed = await ky('https://example.com', { fetch }).json(); })();

ky.extend(defaultOptions)

Create a new

ky
instance with some defaults overridden with your own.

In contrast to

ky.create()
,
ky.extend()
inherits defaults from its parent.

You can pass headers as a

Headers
instance or a plain object.

You can remove a header with

.extend()
by passing the header with an
undefined
value. Passing
undefined
as a string removes the header only if it comes from a
Headers
instance.
import ky from 'ky';

const url = 'https://sindresorhus.com';

const original = ky.create({ headers: { rainbow: 'rainbow', unicorn: 'unicorn' } });

const extended = original.extend({ headers: { rainbow: undefined } });

const response = await extended(url).json();

console.log('rainbow' in response); //=> false

console.log('unicorn' in response); //=> true

ky.create(defaultOptions)

Create a new Ky instance with complete new defaults.

import ky from 'ky';

// On https://my-site.com

const api = ky.create({prefixUrl: 'https://example.com/api'});

(async () => { await api.get('users/123'); //=> 'https://example.com/api/users/123'

await api.get('/status', {prefixUrl: ''});
//=> 'https://my-site.com/status'

})();

defaultOptions

Type:

object

ky.HTTPError

Exposed for

instanceof
checks. The error has a
response
property with the
Response
object
.

ky.TimeoutError

The error thrown when the request times out.

ky.stop

A

Symbol
that can be returned by a
beforeRetry
hook to stop the retry. This will also short circuit the remaining
beforeRetry
hooks.
import ky from 'ky';

(async () => { await ky('https://example.com', { hooks: { beforeRetry: [ async ({request, options, error, retryCount}) => { const shouldStopRetry = await ky('https://example.com/api'); if (shouldStopRetry) { return ky.stop; } } ] } }); })();

Tips

Sending form data

Sending form data in Ky is identical to

fetch
. Just pass a
FormData
instance to the
body
option. The
Content-Type
header will be automatically set to
multipart/form-data
.
import ky from 'ky';

(async () => { // multipart/form-data const formData = new FormData(); formData.append('food', 'fries'); formData.append('drink', 'icetea');

await ky.post(url, {
    body: formData
});

})();

If you want to send the data in

application/x-www-form-urlencoded
format, you will need to encode the data with
URLSearchParams
.
import ky from 'ky';

(async () => { // application/x-www-form-urlencoded const searchParams = new URLSearchParams(); searchParams.set('food', 'fries'); searchParams.set('drink', 'icetea');

await ky.post(url, {
    body: searchParams
});

})();

Cancellation

Fetch (and hence Ky) has built-in support for request cancellation through the

AbortController
API. Read more.

Example:

import ky from 'ky';

const controller = new AbortController(); const {signal} = controller;

setTimeout(() => { controller.abort(); }, 5000);

(async () => { try { console.log(await ky(url, {signal}).text()); } catch (error) { if (error.name === 'AbortError') { console.log('Fetch aborted'); } else { console.error('Fetch error:', error); } } })();

FAQ

How do I use this in Node.js?

Check out

ky-universal
.

How do I use this with a web app (React, Vue.js, etc.) that uses server-side rendering (SSR)?

Check out

ky-universal
.

How do I test a browser library that uses this?

Either use a test runner that can run in the browser, like Mocha, or use AVA with

ky-universal
. Read more.

How do I use this without a bundler like Webpack?

Upload the

index.js
file in this repo somewhere, for example, to your website server, or use a CDN version. Then import the file.

Alternatively, you can use the

umd.js
file with a traditional

 tag (without 
type="module"
), in which case
ky
will be a global.

How is it different from
got

See my answer here. Got is maintained by the same people as Ky.

How is it different from
axios
?

See my answer here.

How is it different from
r2
?

See my answer in #10.

What does
ky
mean?

It's just a random short npm package name I managed to get. It does, however, have a meaning in Japanese:

A form of text-able slang, KY is an abbreviation for 空気読めない (kuuki yomenai), which literally translates into “cannot read the air.” It's a phrase applied to someone who misses the implied meaning.

Browser support

The latest version of Chrome, Firefox, and Safari.

Node.js support

Polyfill the needed browser global or just use

ky-universal
.

Related

  • ky-universal - Use Ky in both Node.js and browsers
  • got - Simplified HTTP requests for Node.js
  • ky-hooks-change-case - Ky hooks to modify cases on requests and responses of objects

Maintainers

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