code: function isValidSha(str) {
    if (typeof str === 'string' && str.length === 40) {
      const res = str.match(/[0-9a-f]/g);
      return res && res.length === 40;
    }
    return false;
  }
docs: Checks if the specified string is a valid SHA-1 value.
  
  @param {string} str
  @returns {boolean} `true` if `str` represents a valid SHA-1, otherwise `false`