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

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
• Retries failed requests
• JSON option
• Timeout support
• URL prefix option
• Instances with custom defaults
• Hooks

Install

$ npm install ky

Download

• Normal
• Minified

CDN

• jsdelivr
• unpkg

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<string, string | number | boolean> | Array<Array<string | number | boolean>> | 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<string, Function[]>
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 the normalized request and options, the failed response, an error instance and the retry count as arguments. You could, for example, modify request.headers here.

import ky from 'ky';

(async () => {
	await ky('https://example.com', {
		hooks: {
			beforeRetry: [
				async ({request, response, options, errors, 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 a HTTPError for error responses (non-2xx status codes).

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`);
		}
	});
})();

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, response, options, errors, 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.

<script type="module">
import ky from 'https://cdn.jsdelivr.net/npm/ky@latest/index.js';

(async () => {
	const parsed = await ky('https://jsonplaceholder.typicode.com/todos/1').json();

	console.log(parsed.title);
	//=> 'delectus aut autem
})();
</script>

Alternatively, you can use the umd.js file with a traditional <script> tag (without type="module"), in which case ky will be a global.

<script src="https://cdn.jsdelivr.net/npm/ky@latest/umd.js"></script>
<script>
(async () => {
	const parsed = await ky('https://jsonplaceholder.typicode.com/todos/1').json();

	console.log(parsed.title);
	//=> 'delectus aut autem
})();
</script>

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

Maintainers

• Sindre Sorhus
• Szymon Marczak
• Seth Holladay