fetch-har

Make a fetch request from a HAR definition.

Features

• Supports Node 14+ (including the native fetch implementation in Node 18!).
• Natively works in all browsers that support fetch without having to use any polyfils.
• Tested across Chrome, Safari, Firefox on Mac, Windows, and Linux.
• Requests can be mocked with nock or fetch-mock.

Installation

npm install --save fetch-har

Usage

require('isomorphic-fetch');

// If executing from an environment that doesn't normally provide `fetch()` we'll automatically
// polyfill in the `Blob`, `File`, and `FormData` APIs with the optional `formdata-node` package
// (provided you've installed it).
const fetchHAR = require('fetch-har').default;
// import fetchHAR from 'fetch-har'); // Or if you're in an ESM codebase.

const har = {
  log: {
    entries: [
      {
        request: {
          headers: [
            {
              name: 'Authorization',
              value: 'Bearer api-key',
            },
            {
              name: 'Content-Type',
              value: 'application/json',
            },
          ],
          queryString: [
            { name: 'a', value: 1 },
            { name: 'b', value: 2 },
          ],
          postData: {
            mimeType: 'application/json',
            text: '{"id":8,"category":{"id":6,"name":"name"},"name":"name"}',
          },
          method: 'POST',
          url: 'http://httpbin.org/post',
        },
      },
    ],
  },
};

fetchHAR(har)
  .then(res => res.json())
  .then(console.log);

API

If you are executing fetch-har in a browser environment that supports the FormData API then you don't need to do anything. If you arent, however, you'll need to polyfill it.

Unfortunately the most popular NPM package form-data ships with a non-spec compliant API, and for this we don't recommend you use it, as if you use fetch-har to upload files it may not work.

Though we recommend either formdata-node or formdata-polyfill we prefer formdata-node right now as it's CJS-compatible.

Options

userAgent

A custom User-Agent header to apply to your request. Please note that browsers have their own handling for these headers in fetch() calls so it may not work everywhere; it will always be sent in Node however.

await fetchHAR(har, { userAgent: 'my-client/1.0' });

files

An optional object map you can supply to use for multipart/form-data file uploads in leu of relying on if the HAR you have has data URLs. It supports Node file buffers and the File API.

await fetchHAR(har, { files: {
  'owlbert.png': await fs.readFile('./owlbert.png'),
  'file.txt': document.querySelector('#some-file-input').files[0],
} });

If you don't supply this option fetch-har will fallback to the data URL present within the supplied HAR. If no files option is present, and no data URL (via param.value) is present in the HAR, a fatal exception will be thrown.

multipartEncoder

❗ If you are using fetch-har in Node you may need this option to execute multipart/form-data requests!

If you are running fetch-har within a Node environment and you're using node-fetch@2, or another fetch polyfill that does not support a spec-compliant FormData API, you will need to specify an encoder that will transform your FormData object into something that can be used with Request.body.

We recommend form-data-encoder.

const { FormDataEncoder } = require('form-data-encoder');

await fetchHAR(har, { multipartEncoder: FormDataEncoder });

You do not, and shouldn't, need to use this option in browser environments.

init

This optional argument lets you supply any option that's available to supply to the Request constructor.

await fetchHAR(har, {
  init: {
    headers: new Headers({
      'x-custom-header': 'buster',
    }),
  },
})

❗ Note that if you supply body or credentials to this option they may be overridden by what your HAR requires.