var /*Page*/first = app.activeDocument.pages.itemByName("4"); 
var /*Page*/second = app.activeDocument.pages.itemByName("5"); 
exchangePages(/*Page*/first, /*Page*/second); 
 
/*Boolean*/function exchangePages(/*Page*/first, /*Page*/second){ 
    try{ 
        var /*Page*/p = null; 
        if (first.documentOffset === 0) 
            p = app.activeDocument.pages.item(2); 
        else 
            p = app.activeDocument.pages.item(first.documentOffset+1); 
            first.move(LocationOptions.BEFORE,second); 
            second.move(LocationOptions.BEFORE,p);         
    } 
    catch (error){ 
        alert(error.message); 
    } 
} 

// AFTER_SELECTION_CHANGED 
// CC 2020; 
#target indesign-15.064  
// CS 6 not testet!!!!! 
// #target indesign-8.0 
#targetengine "mySelectionChangedSession"   
 
if ((afterSelectionChanged === undefined) || (afterSelectionChanged == null)){ 
    var afterSelectionChanged = new AfterSelectionChanged();  
    if (afterSelectionChanged != null) 
        alert("PageExchange is active"); 
} 
else{ 
    afterSelectionChanged.removeListener(); 
    afterSelectionChanged = null; 
    alert("PageExchange is inactive"); 
} 
    
/*Object*/function AfterSelectionChanged(){  
    var/*EventListener*/ afterSelectionChangedListener = app.activeDocument.eventListeners.add("afterSelectionChanged", listenerTest);   
     
    function listenerTest () {   
        var /*Page*/page = null; 
        if (!("pages" in this)) 
            this.pages = []; 
        if (app.selection.length > 0) 
            page = wpsGetParentPageOfObjectIfPossible(app.selection[0]); 
            if (page != null){ 
                this.pages.push(page); 
                if (this.pages.length > 1){ 
                    exchangePages(this.pages[0], this.pages[1]); 
                    this.pages.length = 0; 
                } 
             app.selection = NothingEnum.NOTHING; 
        } 
    }   
    this.removeListener = function(){  
        if(afterSelectionChangedListener != null)   
            afterSelectionChangedListener.remove();   
    }  
    /*page*/function wpsGetParentPageOfObjectIfPossible(/*object*/o)  
    {  
        try 
        { 
            var /*String*/whatIsIt = null, /*Page*/parentPage = null;  
             
            if (o === undefined)  
                return null; 
            if (o === null)  
                return null; 
            if (!(o.isValid))  
                return null; 
             
            if ("parentPage" in o) 
                return o.parentPage; 
                 
            parentPage = (("parentTextFrames" in o) && (o.parentTextFrames.length >0)) ? o.parentTextFrames[0].parentPage : null; 
             
            if (parentPage != null) 
                return parentPage; 
                 
              while (o != null)  
              {  
                  if ("parentPage" in o) 
                    return  o.parentPage;  
                  var whatIsIt = o.constructor;  
                  switch (whatIsIt) {  
                       case Page : return o;  
                       case Character : o = o.parentTextFrames[0]; break;  
                       case Footnote :; // drop through  
                       case Cell : o = o.insertionPoints[0].parentTextFrames[0]; break;  
                       case Note : o = o.storyOffset.parentTextFrames[0]; break;  
                       case XMLElement :  if (o.insertionPoints[0] != null) { o =  o.insertionPoints[0].parentTextFrames[0]; break; }  
                       case Application : return null;  
                       default: o = o.parent;  
                  }  
                  if (o == null) return null;  
             }  
             return o  
         } 
         catch (error) 
        { 
            alert(error.message + "\nin File: " + error.fileName + "\nZeile: " + error.line); 
            // throw error; 
        } 
        return null; 
    }      
    /*Boolean*/function exchangePages(/*Page*/first, /*Page*/second){  
        try{  
            var /*Page*/p = null;  
            if (first.documentOffset === 0)  
                p = app.activeDocument.pages.item(2);  
            else { 
                if ((first.documentOffset +1) === second.documentOffset){ 
                    second.move(LocationOptions.BEFORE,first); 
                } 
                else{     
                    p = app.activeDocument.pages.item(first.documentOffset+1);  
                    first.move(LocationOptions.BEFORE,second);  
                    second.move(LocationOptions.BEFORE,p); 
                } 
            } 
        }  
        catch (error){  
            alert(error.message);  
        }  
    }  
} 

// AFTER_SELECTION_CHANGED  
// CC 2020;  
// #target indesign-15.064   
// CS 6 not testet!!!!!  
#target indesign-8.0 

// AFTER_SELECTION_CHANGED 
// CC 2020; 
#target indesign-15.064  
// CS 6 not testet!!!!! 
// #target indesign-8.0 
#targetengine "mySelectionChangedSession"   
 
if ((afterSelectionChanged === undefined) || (afterSelectionChanged == null)){ 
    var afterSelectionChanged = new AfterSelectionChanged();  
    if (afterSelectionChanged != null) 
        alert("PageExchange is active"); 
} 
else{ 
    afterSelectionChanged.removeListener(); 
    afterSelectionChanged = null; 
    alert("PageExchange is inactive"); 
} 
    
/*Object*/function AfterSelectionChanged(){  
    var/*EventListener*/ afterSelectionChangedListener = app.eventListeners.itemByName("PageExchange");  
     
    this.pages = []; 
         
    if (afterSelectionChangedListener != null) 
        afterSelectionChangedListener.remove(); 
         
    afterSelectionChangedListener = app.eventListeners.add("afterSelectionChanged", listenerTest);     
    afterSelectionChangedListener.name = "PageExchange"; 
     
    function listenerTest () {   
        if (app.selection.length > 0){ 
            page = wpsGetParentPageOfObjectIfPossible(app.selection[0]); 
            if (page != null){ 
                afterSelectionChanged.pages.push(page); 
                if (afterSelectionChanged.pages.length > 1){ 
                    exchangePages(afterSelectionChanged.pages); 
                } 
             app.selection = NothingEnum.NOTHING; 
            } 
        } 
    }   
    this.removeListener = function(){  
        if(afterSelectionChangedListener != null)   
            afterSelectionChangedListener.remove();  
        if ("pages" in this) 
            this.pages.length = 0;     
    }  
    /*page*/function wpsGetParentPageOfObjectIfPossible(/*object*/o)  
    {  
        try 
        { 
            var /*String*/whatIsIt = null, /*Page*/parentPage = null;  
             
            if (o === undefined)  
                return null; 
            if (o === null)  
                return null; 
            if (!(o.isValid))  
                return null; 
             
            if ("parentPage" in o) 
                return o.parentPage; 
                 
            parentPage = (("parentTextFrames" in o) && (o.parentTextFrames.length >0)) ? o.parentTextFrames[0].parentPage : null; 
             
            if (parentPage != null) 
                return parentPage; 
                 
              while (o != null)  
              {  
                  if ("parentPage" in o) 
                    return  o.parentPage;  
                  var whatIsIt = o.constructor;  
                  switch (whatIsIt) {  
                       case Page : return o;  
                       case Character : o = o.parentTextFrames[0]; break;  
                       case Footnote :; // drop through  
                       case Cell : o = o.insertionPoints[0].parentTextFrames[0]; break;  
                       case Note : o = o.storyOffset.parentTextFrames[0]; break;  
                       case XMLElement :  if (o.insertionPoints[0] != null) { o =  o.insertionPoints[0].parentTextFrames[0]; break; }  
                       case Application : return null;  
                       default: o = o.parent;  
                  }  
                  if (o == null) return null;  
             }  
             return o  
         } 
         catch (error) 
        { 
            alert(error.message + "\nin File: " + error.fileName + "\nZeile: " + error.line); 
            // throw error; 
        } 
        return null; 
    }      
    /*Boolean*/function exchangePages(){  
        try{  
            var /*Page*/p = null, /*Page*/first = afterSelectionChanged.pages[0], /*Page*/second = afterSelectionChanged.pages[1];  
            if (first.documentOffset === 0)  
                p = app.activeDocument.pages[1];  
                 
            if ((first.documentOffset +1) === second.documentOffset){ 
                second.move(LocationOptions.BEFORE,first); 
            } 
            else{     
                p = app.activeDocument.pages[first.documentOffset-1];  
                first.move(LocationOptions.BEFORE,second);  
                second.move(LocationOptions.AFTER,p); 
            }             
        }  
        catch (error){  
            alert(error.message);  
        }  
        afterSelectionChanged.pages.length = 0; 
    }  
} 

var page1 = app.documents[0].selection[0]; 

var page2 = app.documents[0].selection[1];