Method setRequestHeader

src/Fetch.js:96–101

* Sets the value of an HTTP request header. * @param {string} header The name of the header. * @param {string} value The value of the header.

(header, value)

   * @param {string} value The value of the header.
   */
  setRequestHeader(header, value) {
    if (this.readyState !== 1) {
      throw new Error('setRequestHeader can only be called when state is OPENED.');
    }
    this._headers[header] = value;
  }

  /**
   * This method is not effectively implemented because Fetch API relies on the