responseinterceptor.js

const replaceProperty = (obj, propName, descriptorOverrides = {}) => {
  return Object.defineProperty(obj, propName, {
    // Copy over the existing descriptors (writable, enumerable, configurable, etc)
    ...(Object.getOwnPropertyDescriptor(obj, propName) || {}),
    // Add our overrides (e.g. value, get())
    ...descriptorOverrides
  })
}

const replaceWithProxy = (obj, propName, handler) => {
  const proxyObj = new Proxy(obj[propName], handler);
  replaceProperty(obj, propName, { value: proxyObj });
  return true;
}

const openProxyHandler = {
  apply: function(target, ctx, args) {
    const [method, URL, async, user, password] = args;
    ctx.addEventListener('loadend', function () {
      // Get the raw header string
      const headers = ctx.getAllResponseHeaders();

      // Convert the header string into an array of individual headers
      const arr = headers.trim().split(/[\r\n]+/);

      // Create a map of header names to values
      const headerMap = [];
      arr.forEach(function (line) {
        const parts = line.split(': ');
        const header = parts.shift();
        const headerObject = { [header]: parts.join(': ')};
        headerMap.push(headerObject);
      });

      const payload = {
        status: ctx.status,
        statusText: '',
        responseURL: ctx.responseURL,
        responseType: ctx.responseType,
        response: ctx.response,
        responseHeaders: headerMap,
        requestHeaders: ctx.requestHeaders,
        method: ctx.method,
        data: ctx.data,
      };
      if (ctx.responseType === '' || ctx.responseType === 'text') {
        payload.responseText = ctx.responseText;
      }
      window.postMessage({ type: 'MAIN_NETWORK_RESPONSE', payload }, '*');
      console.log(payload);
    }, false);
    ctx.method = method;
    return Reflect.apply(target, ctx, args);
  }
}

const setRequestHeaderProxyHandler = {
  apply: function(target, ctx, args) {
    if (!ctx.requestHeaders) {
      ctx.requestHeaders = [];
    }
    const [name, value] = args;
    const header = { [name]: value };
    ctx.requestHeaders.push(header);
    return Reflect.apply(target, ctx, args);
  }
};

const sendProxyHandler = {
  apply: function(target, ctx, args) {
    ctx.data = (args || [])[0];
    return Reflect.apply(target, ctx, args);
  }
}

replaceWithProxy(XMLHttpRequest.prototype, 'open', openProxyHandler);
replaceWithProxy(XMLHttpRequest.prototype, 'setRequestHeader', setRequestHeaderProxyHandler);
replaceWithProxy(XMLHttpRequest.prototype, 'send', sendProxyHandler);