Sharepoint - How to update multiple items in sharepoint list online using javascript

I have a list called rohit_list1 on which i am updating title for all the items with ID greater than 15. You Write your own CAML query to get ID's.

Design :

<input type="button" value="updateMultipleListItems" onclick="getItemsToBeUpdated()" />

JSOM Code :

<script type="text/javascript">
    var collListItemToBeUpdated = "";
    var listItemToBeUpdated = "";
    function getItemsToBeUpdated() <--- this function called on button click to get ID's
    {
         var clientContext = new SP.ClientContext.get_current();
         var oList = clientContext.get_web().get_lists().getByTitle('rohit_list1');
         var camlQuery = new SP.CamlQuery();
         camlQuery.set_viewXml('<View><Query><Where><Geq>' +
            '<FieldRef Name=\'ID\'/><Value Type=\'Number\'>15</Value>' +
            '</Geq></Where></Query></View>');
         collListItemToBeUpdated = oList.getItems(camlQuery);
         clientContext.load(collListItemToBeUpdated);
         clientContext.executeQueryAsync(getItemsToBeUpdatedSuccess, getItemsToBeUpdatedFailed);
    }
    function getItemsToBeUpdatedSuccess()
    {
         ListItemToBeUpdated= collListItemToBeUpdated.getEnumerator();
         updateMultipleListItems();
    }
    function getItemsToBeUpdatedFailed(sender, args)
    {
        alert('Request failed. ' + args.get_message() + '\n' + args.get_stackTrace());
    }

    function updateMultipleListItems() <--- this function called on successfully getting ID's
    {   
        var itemArray = [];
        var clientContext = SP.ClientContext.get_current();
        var oList = clientContext.get_web().get_lists().getByTitle('rohit_list1');

         while(ListItemToBeUpdated.moveNext())
         {
            var oItem = ListItemToBeUpdated.get_current();
            var oListItem = oList.getItemById(oItem.get_id());
            oListItem.set_item('Title', 'Updated ...!');  
            oListItem.update();
            itemArray.push(oListItem);
            clientContext.load(itemArray[itemArray.length-1]);
         }  
        clientContext.executeQueryAsync(updateMultipleListItemsSuccess, updateMultipleListItemsFailed);
    }
    function updateMultipleListItemsSuccess() 
    {    
        alert('Items Updated');
    }

    function updateMultipleListItemsFailed(sender, args) 
    {    
        alert('Request failed. ' + args.get_message() + '\n' + args.get_stackTrace());
    }
    </script>

Since you haven't told us which API you prefer, below is demonstrated how to retrieve and update list items using JSOM API:

function getListItems(listTitle)
{
    var deferred = $.Deferred();
    var ctx = SP.ClientContext.get_current();
    var list = ctx.get_web().get_lists().getByTitle(listTitle);
    var items = list.getItems(SP.CamlQuery.createAllItemsQuery());
    ctx.load(items);
    ctx.executeQueryAsync(function() {
        deferred.resolve(items);
    },
    function(sender,args){
        deferred.reject(sender, args);
    });
    return deferred.promise();
}


function updateListItems(items) 
{
     var deferred = $.Deferred();
     var ctx = items.get_context(); 
     var itemProperties = {'Title': 'John Doe'}; 

     //prepare to update list items 
     items.get_data().forEach(function(item){
           for(var propName in itemProperties) {
               item.set_item(propName, itemProperties[propName]) 
           }
           item.update();
     });

     //submit request
     ctx.executeQueryAsync(function() {
        deferred.resolve(items);
     },
     function(sender,args){
        deferred.reject(sender, args);
     });
     return deferred.promise();
}

Usage

//update Title for all items in Contacts list
getListItems('Contacts').then(updateListItems).then(logSuccess,logError);

function logError(sender,args){
   console.log('An error occured: ' + args.get_message());
}

function logSuccess(sender,args){
   console.log('Updated.');
}