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sindresorhus/ ky (v0.28.6) 7 days ago
JavaScript http-client fetch TypeScript js npm-package http-request whatwg-fetch
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About the developer

sindresorhus
6.9K Stars 250 Forks MIT License 235 Commits 24 Opened issues

Description

🌳 Tiny & elegant JavaScript HTTP client based on the browser Fetch API

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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

Coverage Status

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

fetch
polyfill and 
globalThis
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';


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


console.log(json);
//=> {data: '🦄'}

With plain 

fetch
, it would be: 
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 json = await response.json();


console.log(json);
//=> {data: '🦄'}

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

import ky from 'https://cdn.skypack.dev/ky?dts';

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


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


const response2 = 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';


const json = 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');
            }
        ]
    }
});


const response = 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, the error will be of type 

HTTPError
and the 
Response
object 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. In that case, the error will not be an instance of 
HTTPError
.

You can prevent Ky from retrying the request by throwing an error. Ky will not handle it in any way and the error will be propagated to the request initiator. The rest of the 

beforeRetry
hooks will not be called in this case. Alternatively, you can return the 
ky.stop
 symbol to do the same thing but without propagating an error (this has some limitations, see 
ky.stop
docs for details). 
import ky from 'ky';


const response = 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';


const response = 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.

Note: If 

false
, error responses are considered successful and the request will not be retried.
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';


const response = 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';


const json = 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';


const json = 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'});


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


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

defaultOptions

Type: 

object

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.

Note: Returning this symbol makes Ky abort and return with an 

undefined
response. Be sure to check for a response before accessing any properties on it or use optional chaining. It is also incompatible with body methods, such as 
.json()
or 
.text()
, because there is no response to parse. In general, we recommend throwing an error instead of returning this symbol, as that will cause Ky to abort and then throw, which avoids these limitations.

A valid use-case for 

ky.stop
is to prevent retries when making requests for side effects, where the returned data is not important. For example, logging client activity to the server. 
import ky from 'ky';


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


// Note that response will be undefined in case ky.stop is returned.
const response = await ky.post('https://example.com', options);


// Using .text() or other body methods is not suppported.
const text = await ky('https://example.com', options).text();

HTTPError

Exposed for 

instanceof
checks. The error has a 
response
property with the 
Response
object, 
request
property with the 
Request
object, and 
options
property with normalized options (either passed to 
ky
when creating an instance with 
ky.create()
or directly when performing the request).

TimeoutError

The error thrown when the request times out. It has a 

request
property with the 
Request
object.

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';


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


const response = 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';


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


const response = 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);


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?

Make sure your code is running as a JavaScript module (ESM), for example by using a 

 tag in your HTML document. Then Ky can be imported directly by that module without a bundler or other tools.



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 globals 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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