axios interceptors

experimentInterceptor.js

import axios from 'axios';

export const experimentsInterceptor = () => {
  const getExperiments = () => {
    const [, params] = window.location.search.split('?');
    const experiments = params.split('ex.');

    const values = experiments.reduce((tally, item) => {
      if (item.match(/^[A-Z][A-Z][A-Z]\d\d/)) {
        const newItem = item.replace('&', '');
        tally.push(newItem);
      }

      return tally;
    }, []);

    const set = new Set(values);

    return [...set];
  };

  axios.interceptors.request.use(
    config => {
      const experiments = getExperiments();

      if (experiments.length !== 0) {
        config.headers['my-custom-header'] = experiments.join(',');
      }

      return config;
    },
    error => {
      // Do something with request error
      return Promise.reject(error);
    }
  );
};

experimentInterceptor.spec.js

import axios from 'axios';
import axiosMock from 'jest-mock-axios';

describe('experimentInterceptor', () => {
  const BASE_URL_WITH_PARAMS = 'http://localhost:3000/some_route/child_route?q=something&ex.RGB00=2&ex.ABC99=3';
  const API_ENDPOINT = 'http://localhost:9000/some_route';

  beforeEach(() => {
    axiosMock.reset();
  });

  it('should add my-custom-header header to any api request when the URL has experiment params', async () => {
    mockWindow(BASE_URL_WITH_PARAMS);
    experimentsInterceptor();

    axiosMock.get(API_ENDPOINT);

    const config = await axios.interceptors.request.handlers[0].fulfilled({
      url: API_ENDPOINT,
      headers: {}
    });

    expect(config.headers).toEqual({
      'my-custom-header': 'RGB00=2,ABC99=3'
    });
  });
});

windowMock.js

const mockWindow = search => {
  Object.defineProperty(global, 'window', {
    value: {
      location: {
        search
      }
    },
    writable: true
  });
};