I have values of my CSV stored in a string variable named 'csv'. Now i want to download the content of this variable with click of button('submit') on page but i don't want to redirect to another page.The best is by using java script.PS: the variable is stored in my component it is not a page.
Controller code:

public class PaginationForComponent {
    public PaginationForComponent(){
    allContactList = new list<wrapper>();
    myOrder = 'desc';
    sortField='name';
    PageNumber = 1;
    alphabet = new list<string>{'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z','Others','All'};
    RecordsPerPageslist = 10;
    System.debug('constructor called');
    csv='';
  }
  Boolean lstNamePresent=false;
  public String objName{get;set;}
  public String fieldNames{get;set;}
  list<sObject> con = new list<sObject>();
  public String alphaSearchConct{get;set;}
  public string msg {get;set;}
  public Map<id,Boolean> m = new Map<id,boolean>(); 
  list<sObject> sortedList;
  public String myOrder{get;set;}                 // Ascending or Descending order of sorting
  public String sortField{get;set;}               // Field by which sorting should be done
  public boolean selectAll{get;set;}
  public list<String> alphabet{get;set;}
  public list<sObject> cont;
  public list<wrapper> allContactList{get;set;}
  public list<wrapper> ct = new list<wrapper>();
  public list<String> query;
  public String csv{get;set;}
 
  public ApexPages.StandardSetController stdSetController{            //Instantiating a standard set controller
    get{
        if(stdSetController==null){
            //con = Database.query('SELECT '+ fieldNames+' FROM '+ objName );//del it from here update con from script n return allContactList by filling it from there only
            System.debug('con in ssc is : ' + con);
            stdSetController = new ApexPages.StandardSetController(con);
        }
        stdSetController.setPageSize(RecordsPerPageslist);        //Limiting Number of records to be displayed per page 
        System.debug('stdSetController called and fieldNames are : ' + allContactList);
        return stdSetController;   
    }
    set;
  }
  public void SelectedListContacts(){         // Select contacts and save them in a map  
    for(wrapper wc:allContactList){
        m.put(wc.con.id,wc.isSelected);
        if(wc.isSelected==false){
            selectAll=false;
         }
    }
  }
  public void SelectedAllContacts(){          //To select all contacts in a page
    System.debug(selectAll);
    allContactList.clear();
    for(sObject c:(list<sObject>)stdSetController.getRecords()){
        allContactList.add(new wrapper(c));
    }
    if(selectAll==true){
        for(wrapper wc:allContactList){
            m.put(wc.con.id,wc.isSelected=true);
    }
   }
    else{
      for(wrapper wc:allContactList)
          m.put(wc.con.id,wc.isSelected=false);
   }
  }
  public String[] getqueryList(){
    query = fieldNames.split(',');
    for(String s:query){
      if(s=='lastname'){
        lstNamePresent=true;
      }
  }

}
  public list<wrapper> getWrapperContacts(){      //List of wrapper class to display in table
    return allContactList;
  }

  public Integer stdSize(){
    Integer i = stdSetController.getRecords().size();
    return i;
  }

  public void docReady(){
    con = Database.query('SELECT '+ fieldNames+' FROM '+ objName );
    System.debug('docReady con is ' + con);
    for(sObject c:(list<sObject>)stdSetController.getRecords())
          allContactList.add(new wrapper(c));
    System.debug('docReady allContactList is ' + allContactList);
  }

public void submit() {
    Set<id> ids = new set<id>();
    for(id i:m.keySet()){
        if(m.get(i)==true){ 
        ids.add(i);
        }
    }
    String queryStr = 'SELECT ' + fieldNames + ' FROM ' + objName + ' WHERE id IN :ids';
    sObject[] c = Database.query(queryStr);
    String temp = '';
    for(Integer i=0;i<c.size();i++){
    for(String s: query){
       temp = String.valueOf((c[i].get(s)));
       // System.debug('before escape csv temp is ' + temp);
        if(temp!=null){
            temp = temp.escapeCsv();}
       // System.debug('temp after escapeCsv() is ' + temp);
        csv += temp;
       // System.debug('str is '+str);
        csv += ', ';
    }
  }
}
// To convert to CSV file
 
public String getgenerateCSV() {
  System.debug('csv is :' + csv);
  return csv;
}
/*public String[] getqueries(){
  System.debug(csvQuery);
  return csvQuery;
}*/
  public class wrapper{
    public boolean isSelected{get;set;}  
    public sObject con{get;set;}  
    public   wrapper(sObject con){
            //System.debug('constructor of wrapper class called ');
            isSelected = false;
            this.con = con;
        }
  }
}

Component code:

<apex:component controller="PaginationForComponent" allowDml="true">

    <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js">
    </script>
    <script>
    	function SuccessFailure(msg) {
        	if(msg == '') {
            	window.top.location.reload()
            } else {
            	alert(msg);
            }
        }
        function cannotFind(msg){
            if(msg!=null)
                alert(msg);
        }
        $(document).ready(function(){
            funAtLast();
        });
    </script>
    <apex:attribute name="objectName" description="The object's name" type="String" required="true" assignTo="{!objName}"/>
    <apex:attribute name="fieldName" description="Fields to be displayed" type="String" required="true" assignTo="{!fieldNames}"/>
    <apex:outputPanel id="form">
        <apex:actionFunction action="{!docReady}" name="funAtLast" reRender="form,alpha,table,button"/>
        <style>
    .bPageBlock .pbBody .dataCol {
        border:0px;
    }
    .bPageBlock .pbBody .labelCol { 
        border:0px;
    }
	</style>
       <!-- <apex:commandButton value="Process" reRender="form,alpha,table,button"/>-->
        <apex:outputPanel rendered="{!allContactList.size!=0}" id="page">
            <!-- For alphabetic search-->
                <div align="right" >
                        <apex:repeat value="{!alphabet}" var="alph" >
                            <apex:commandLink value="{!alph}  " action="{!alphaSearch}" oncomplete="cannotFind('{!msg}');" reRender="table,button" id="cs" > &ensp;
                                <style type="text/css">
                                    #cs:hover{
                                        background-color: #b3ffff;
                                    }
                                </style>
                                <apex:param name="a" value="{!alph}" assignTo="{!alphaSearchConct}"/>
                            </apex:commandLink>
                        </apex:repeat>
                </div>
            <apex:pageBlock id="table">
                <!-- To delete selected records-->
                <apex:commandButton action="{!DelSelected}" value="Delete Selected" oncomplete="SuccessFailure('{!msg}');"/>
                <!-- Button for csv download -->
                <apex:commandButton action="{!submit}" value="Download CSV" reRender="none"/>
                <apex:pageMessages rendered="true" id="Msg"/>
                <apex:PageBlockTable value="{!WrapperContacts}" var="contacts">
                    <!-- To Edit and Delete a record -->
                   <apex:column headerValue="Action">
                        <apex:outputLink value="{!URLFOR($Action[objectName].Edit,contacts.con.id)}">
                            Edit |
                        </apex:outputLink>
                        <apex:outputLink value="{!URLFOR($Action[objectName].Delete,contacts.con.id)}"> 
                            Del |
                        </apex:outputLink>
                    </apex:column>
                    <apex:column >
                    <apex:facet name="header">
                            <apex:inputCheckbox value="{!selectAll}">  
                                <apex:actionSupport event="onclick" action="{!SelectedAllContacts}" reRender="table"/>
                                </apex:inputCheckbox>  
                            </apex:facet>
                        <apex:inputCheckbox value="{!contacts.isSelected}">
                            <apex:actionSupport event="onclick" action="{!SelectedListContacts}" reRender="none" />
                        </apex:inputCheckbox> 
                    </apex:column>
                    <apex:repeat value="{!queryList}" var="fldNames">
                        <apex:column >
                            <apex:facet name="header">
                                <apex:commandLink value="{!fldNames}" action="{!toggleSort}" reRender="table">
                                    <apex:param name="sortField" value="{!fldNames}" assignTo="{!sortField}" />
                                    <apex:param name="myOrder" value="{!IF(myOrder == 'DESC', 'ASC','DESC')}" assignTo="{!myOrder}" />
                                </apex:commandLink>
                            </apex:facet>
                            {!contacts.con[fldNames]}
                        </apex:column>
                    </apex:repeat>
                </apex:PageBlockTable>
            </apex:pageBlock>
            <apex:outputPanel id="button"> 
                <div align = "center" >
                    <!-- To return to first page of records-->
                    <apex:commandButton action="{!first}" value="<<" title="First Page" disabled="{!!HasPrevious}" reRender="table,button"/>
                    <!-- To return to Previous page of records-->
                    <apex:commandButton action="{!previous}" value="Previous" disabled="{!!HasPrevious}" reRender="table,button"/>
                    <!-- To return to next page of records-->
                    <apex:commandButton action="{!next}" value="Next >" disabled = "{!!HasNext}" reRender="table,button"/>
                    <!-- To return to last page of records-->
                    <apex:commandButton action="{!last}" value=">>" title="Last Page" disabled="{!!HasNext}" reRender="table,button"/>
                    <!-- InputText to display current page and to navigate to any page number, At righmost side of page-->
                    <span style="float:right">
                        <apex:outputLabel value="Page ">
                        </apex:outputLabel>
                         <!-- To navigate to the page--> 
                        <apex:InputText value="{!PageNumber}" maxLength="4" size="1">
                        <apex:actionSupport event="onchange" action="{!NavigateByText}"  reRender="table,button"/>
                        </apex:InputText>
                         <!-- The above action support is not working-->         
                        <apex:outputLabel value=" of {!TotalPages}">
                        </apex:outputLabel>
                    </span>
                    <!-- To display a list for number of records to be selected per page-->
                    <span style = "float:left">
                        <apex:SelectList value="{!RecordsPerPageslist}" size="1" >
                            <apex:selectOptions value="{!RecordsPerPageOptionList}">    
                            </apex:selectOptions>
                            <apex:actionSupport event="onchange" action="{!ChangeNumberOfRecordsPerPage}" reRender="table,button"/>
                        </apex:SelectList>
                    </span>
                </div>
            </apex:outputPanel>    
        </apex:outputPanel> 
    </apex:outputPanel>
</apex:component>

I have tried to provide only the relevant code, if something irrelevant is present then please ignore that and the values are being inserted in csv variable