text: // Copyright © 2019 The Things Network Foundation, The Things Industries B.V.
  //
  // Licensed under the Apache License, Version 2.0 (the "License");
  // you may not use this file except in compliance with the License.
  // You may obtain a copy of the License at
  //
  //     http://www.apache.org/licenses/LICENSE-2.0
  //
  // Unless required by applicable law or agreed to in writing, software
  // distributed under the License is distributed on an "AS IS" BASIS,
  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  // See the License for the specific language governing permissions and
  // limitations under the License.
  
  const CHAR_BYTES = 4
  
  /**
   * Computes the join EUI prefix given `joinEUI` and its `length`.
   * @param {string} joinEUI - The join EUI.
   * @param {number} length - The length of the prefix.
   * @returns {string} - The join EUI prefix.
   */
  function computePrefix(joinEUI, length = 0) {
    // TODO: Support generating all prefixes that dont fulfil `length % CHAR_BYTES === 0`
    // (https://github.com/TheThingsNetwork/lorawan-stack/issues/1263)
    return joinEUI.slice(0, Math.ceil(length / CHAR_BYTES))
  }
  
  export default computePrefix
  