Is there any simply (probably key-value) storage in ExtendScript, i.e. "localStorage", "prefs", "settings"?

Sounds to me as if the OP is looking for something like the Persistent Global Variables, we have in Acrobat JavaScript. But, as far as I have seen so far, there is no such concept in Extendscript (but I may be wrong on that).

Actually that what custom script options are they are global across all document.  You can have them be persistent for just the Photoshop session or all Photoshop sessions.  The following script uses a custom script option that last just during a Photoshop session.  For cycling thought sets of tool presets sets. Each tools preset set would have its own custom option and script.  The Script is designed to actually in two parts the function designed to be included into the cycling scripts that set the parameters up for the function the uses the included function. Each script would relate to a tool preset set for a tool like the brush tool.  The function included has all the code and creates the custom script option. Which is an index used to address the presets array.

/* ======================================================================================
              Cycling Forward and Backward through Sets of Tool Presets 
=========================================================================================
2017  John J. McAssey (JJMack)
=========================================================================================
Naming Your Script so that it identify the tool and Presets Set will be helpful.
    Copy this script to a new Name for each set of presets you want to cycle through.
  Run that script via shortcut keys. Set two Shortcuts keys 
  F(n) Forward  Modifier+F(n) Backward
  There are three required parameters for the cycling function:
  1.) Correct Photoshop Tools Name 
  2.) Presets Set file name the * part of the *.tpl file
  The *.tpl file must reside in the scripts folder
  3.) Array of preset names in your desired cycling order
=========================================================================================
Note: This script only deals with Tool Preset files .tpl for tools preset are easily 
  reset back to Adobe's defaults using the Preset manager. Tool presets may require
  other Photoshop add-ons like brush .abr, patterns .pat, swatch .aco, etc files to
  also be loaded this script will not load them this script will only load .tpl 
  files if there is a need too. You must add what your presets require to Photoshop
======================================================================================== */
#target photoshop;
app.bringToFront();
// Required three parameters  tool,Set,list
var tool = 'paintbrushTool';                     // Photoshop Tool name your Presets set is for. Only one tool's presets
// This sample script presets were downloaded from DeviantArt brushes "The Sketch Arsenal" "the_sketch_arsenal_by_thatld.tpl"
// http://thatld.deviantart.com/art/The-Sketch-Arsenal-161678023 Download link on Top Right of the Page not the one on the bottom
var presetSet  = 'the_sketch_arsenal_by_thatld'; // Presets set name *.tpl file need to be same folder as this Photoshop script.
var presetNames = [                              // Preset names list start. Presets you want to cycle through. Set can have more. 
  'Color Brush - Flat',
  'Color Brush - Magic Edge',
  'Color Pencil - Hard',
  'Color Pencil - Soft',
  'Drawing Pencil - B Lead',
  'Drawing Pencil - Blue Line',
  'Drawing Pencil - H Lead',
  'Linework Pen - Fine',
  'Marker - Lower the Flow to Dry',
  'Shading Brush - Pressure Hold',
  'Shading Brush - Soft Texture',
  'Shading Pencil - General',
  'Shading Pencil - Hard',
  'Shading Pencil - Soft',
  'Sketch Pencil - H Lead',
  'Sketch Pencil - The Ultimate!',
  'Watercolor Brush - General'
  ];                                          // Presets names list end. Order the way you want to cycle through them
// End Required Parameters
cycle(tool,presetSet,presetNames);                  // Cycle Forward and Backward through tool presets set names
// End of Script
// =================================================== Main function ======================================================== //
function cycle(toolName,toolPresetSet,toolPresetNames){
  if (currentToolName()!=toolName) { // if user is switching tools try to else switch tool preset
  try {selectTool(toolName);} // Insure the tool is select so preset can be selected
  catch(e) {alert("Unable to Select the Tool "+toolName); return;} // Tool name wrong or unavailable 
  //if (app.toolSupportsBrushes(app.currentTool)) app.runMenuItem(charIDToTypeID(('TglB'))); //Toggle Brush Palette
  return; // Just switch to the tools current setting 
  }
  var desc = new ActionDescriptor(); // Set up Photoshop to remember variables
  try {var desc = app.getCustomOptions('Cycle'+toolPresetSet);} // Try to get CustomOption for cycling this tool presets set
  catch(e){ // Each Photoshop session this should fail first time reset
  try {selectToolPreset(toolPresetNames[0]);} // Insure Tool Presets Set has been loaded 
  catch(e) { // Will fail if tools presets set is not loaded
  if (loadToolPresetSet(toolPresetSet)) { // Load Tool presets set
  try {selectToolPreset(toolPresetNames[0]);} // Load sets first preset
  catch(e) {alert("Was unable to Select the Tools Preset "+toolPresetNames[0]); return;} // Failed to select preset
  }
  else {alert("Was unable to load Tools Presets Set "+toolPresetSet); return;} // Failed to load tools presets set
  }
  desc.putInteger(0,0); // This line save the variable while Photoshop is open,
  app.putCustomOptions('Cycle'+toolPresetSet,desc,false );// Initialize presets set CustomOption for cycling
  desc = app.getCustomOptions('Cycle'+toolPresetSet); // Get CustomOption Cycle starting point
        }
  var presetNumber = desc.getInteger(0); // Get the preset index
  if (ScriptUI.environment.keyboardState.ctrlKey||ScriptUI.environment.keyboardState.altKey||
  ScriptUI.environment.keyboardState.shiftKey) { // Previous preset if Ctrl or Alt or Shift key is down
  presetNumber = presetNumber-2; // Back up two preset for it will be bumped one
  if (presetNumber<0){presetNumber=toolPresetNames.length-1;} // Set preset index to the end of the list
  }
  if (presetNumber<toolPresetNames.length){desc.putInteger(0,presetNumber+1);} // Update preset index number
  else {presetNumber=0; desc.putInteger(0,1);} // Reset preset index pointer to the begging of the list
  app.putCustomOptions('Cycle'+toolPresetSet,desc,false); // Put Update the Custom option
  try {selectToolPreset(toolPresetNames[presetNumber]);} // Set tool with preset
  catch(e) {
  if (loadToolPresetSet(toolPresetSet)) { // Load Tool presets set Tool presets may have reset
  try {selectToolPreset(toolPresetNames[presetNumber]);} // Set tool with preset
  catch(e) {alert("Was unable to Select the Tools Preset "+toolPresetNames[presetNumber]); return;} // Failed to select
  }
  else {alert("Was unable to load Tools Presets Set "+toolPresetSet); return;} // Failed to load tools presets set
  }
};
// =================================================== Helper functions ===================================================== //
function selectTool(tool) {
    var desc9 = new ActionDescriptor();
        var ref7 = new ActionReference();
        ref7.putClass( app.stringIDToTypeID(tool) );
    desc9.putReference( app.charIDToTypeID('null'), ref7 );
    executeAction( app.charIDToTypeID('slct'), desc9, DialogModes.NO );
};
function selectToolPreset(PresetName) {
  var desc = new ActionDescriptor();
  var ref = new ActionReference();
  ref.putName( stringIDToTypeID( "toolPreset" ), PresetName );
  desc.putReference( charIDToTypeID( "null" ), ref );
  executeAction( charIDToTypeID( "slct" ), desc, DialogModes.NO );
}
function loadToolPresetSet(SetName) {
  returncode = true;
  var scriptLocation = String(findScript());
  var path = scriptLocation.substr(0, scriptLocation.lastIndexOf("/") + 1 ) ;
  var SetFile = new File(path + SetName + ".tpl");   // Requited to be in the script's folder
  if (!SetFile.exists) { returncode = false; }
  else {
  var desc = new ActionDescriptor();
  var ref = new ActionReference();
  ref.putProperty( charIDToTypeID( "Prpr" ), stringIDToTypeID( "toolPreset"  ));
  ref.putEnumerated( charIDToTypeID( "capp" ), charIDToTypeID( "Ordn" ), charIDToTypeID( "Trgt"  ) );
  desc.putReference( charIDToTypeID( "null" ), ref );
  desc.putPath( charIDToTypeID( "T   " ), new File( SetFile ) );
  desc.putBoolean( charIDToTypeID( "Appe" ), true );
  try {executeAction( charIDToTypeID( "setd" ), desc, DialogModes.NO );}
  catch(e) { returncode = false; }
  }
  return returncode ;
}
function findScript() {// Find the location where this script resides
  var where = "";
  try { FORCEERROR = FORCERRROR;}
  catch(err) { where = File(err.fileName);}
  return where ;
}
function currentToolName() {
  var ref = new ActionReference();
  ref.putProperty(stringIDToTypeID("property"), stringIDToTypeID("tool"));
  ref.putEnumerated( charIDToTypeID("capp"), charIDToTypeID("Ordn"), charIDToTypeID("Trgt") );
  var applicationDesc = executeActionGet(ref);
  //alert(typeIDToStringID(applicationDesc.getEnumerationType(stringIDToTypeID("tool"))));
  return(typeIDToStringID(applicationDesc.getEnumerationType(stringIDToTypeID("tool"))));
}
/* Photoshop tool names
'moveTool'                     'cloneStampTool'            'typeCreateOrEditTool'
'marqueeRectTool'              'patternStampTool'          'typeVerticalCreateOrEditTool'
'marqueeEllipTool'             'historyBrushTool'          'typeCreateMaskTool'
'marqueeSingleRowTool'         'artBrushTool'              'typeVerticalCreateMaskTool'
'marqueeSingleColumnTool'      'eraserTool'                'pathComponentSelectTool'
'lassoTool'                    'backgroundEraserTool'      'directSelectTool'
'polySelTool'                  'magicEraserTool'           'rectangleTool'
'magneticLassoTool'            'gradientTool'              'roundedRectangleTool'
'quickSelectTool'              'bucketTool'                'ellipseTool'
'magicWandTool'                'blurTool'                  'polygonTool'
'cropTool'                     'sharpenTool'               'lineTool'
'sliceTool'                    'smudgeTool'                'customShapeTool'
'sliceSelectTool'              'dodgeTool'                 'textAnnotTool'
'spotHealingBrushTool'         'burnInTool'                'soundAnnotTool'
'magicStampTool'               'saturationTool'            'eyedropperTool'
'patchSelection'               'penTool'                   'colorSamplerTool'
'redEyeTool'                   'freeformPenTool'           'rulerTool'
'paintbrushTool'               'addKnotTool'               'handTool'
'pencilTool'                   'deleteKnotTool'            'zoomTool'
'colorReplacementBrushTool'    'convertKnotTool'           'wetBrushTool'

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