Google sheets toggle, hide, show rows.

ToggleRows.js

function onOpen() {
  var sheet = SpreadsheetApp.getActiveSpreadsheet();
  var entries = [{
    name: "Toggle Rows",
    functionName: "toggleRows"
  },{
    name: "Hide Rows",
    functionName: "hideRows"
  },{
    name: "Show Rows",
    functionName: "showRows"
  }];
  sheet.addMenu("Script", entries);
};

function toggleRows() {
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var sheet = ss.getActiveSheet();
  var maxRows = sheet.getMaxRows();
  
  var r = sheet.getRange(1, 1, maxRows+1);
  var values = r.getValues();
  var hideRanges = [];
  var showRanges = [];

  var toggleValue = null;
  var startRow = null;

  var tmp;
  var len = values.length;
  var i;
  for (i = 0; i < len; i++) {
    tmp = values[i][0];
    if (startRow === null && (tmp === '--' || tmp === '||')) {
      startRow = i + 1;
      toggleValue = tmp;
    } else if (startRow !== null && tmp !== toggleValue) {
      if (toggleValue === '--') {
        hideRanges.push([startRow, (i + 1) - startRow]);
      } else {
        showRanges.push([startRow, (i + 1) - startRow])
      }

      if (tmp === '--' || tmp === '||') {
        startRow = i + 1;
        toggleValue = tmp;
      } else {
        startRow = null;
      }
    }
  }

  var customRange = null;
  var range = null;

  i = hideRanges.length;
  while (i--) {
    customRange = hideRanges[i];
    range = sheet.getRange(customRange[0], 1, customRange[1]);
    range.setValue('||');
    sheet.hideRows(customRange[0], customRange[1]);
  }

  i = showRanges.length;
  while (i--) {
    customRange = showRanges[i];
    range = sheet.getRange(customRange[0], 1, customRange[1]);
    range.setValue('--');
    sheet.showRows(customRange[0], customRange[1]);
  }

};

function hideRows() {
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var sheet = ss.getActiveSheet();
  var maxRows = sheet.getMaxRows();

  var r = sheet.getRange(1, 1, maxRows+1);
  var values = r.getValues();
  var startRow = null;

  var tmp;
  var len = values.length;
  var i;
  for (i = 0; i < len; i++) {
    tmp = values[i][0];
    if (startRow === null && (tmp === '--' || tmp === '||')) {
      startRow = i + 1;
    } else if (startRow !== null && (tmp !== '--' && tmp !== '||')) {
      var numRows = (i + 1) - startRow;
      sheet.getRange(startRow, 1, numRows).setValue('||');
      sheet.hideRows(startRow, numRows);
      startRow = null;
    }
  }

};

function showRows() {
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var sheet = ss.getActiveSheet();
  var maxRows = sheet.getMaxRows();

  var r = sheet.getRange(1, 1, maxRows+1);
  var values = r.getValues();
  var startRow = null;

  var tmp;
  var len = values.length;
  var i;
  for (i = 0; i < len; i++) {
    tmp = values[i][0];
    if (startRow === null && (tmp === '--' || tmp === '||')) {
      startRow = i + 1;
    } else if (startRow !== null && (tmp !== '--' && tmp !== '||')) {
      var numRows = (i + 1) - startRow;
      sheet.getRange(startRow, 1, numRows).setValue('--');
      sheet.showRows(startRow, numRows);
      startRow = null;
    }
  }

};