var store1Loaded = false;
var store2Loaded = false;

store1.on('load', function(){
    store1Loaded = true;
});

store2.on('load', function(){
    store1Loaded = true;
});


store1.load();
store2.load();

function WaitForFunction()
{
    if (!store1Loaded || !store2Loaded)) {
       setTimeout( WaitForFunction, 100);
       return;
    }
    AllStoresLoaded();
}

function AllStoresLoaded(){
      //Do Something
}

var store1 = Ext.create('Ext.data.Store', {
    model: myModel,
    storeId: 'store1', // store needs to be done MVC style or have this config
    proxy: {
        type: 'ajax',
        url: 'url...',
        reader: 'json'
    },
    autoLoad: {
        callback: initData // do this function when it loads
    }
});

var store2 = Ext.create('Ext.data.Store', {
    model: myModel,
    storeId: 'store2',
    proxy: {
        type: 'ajax',
        url: 'url...',
        reader: 'json'
    },
    autoLoad: {
        callback: initData // do this function when it loads
    }
});

// the stores to be checked
var myComboStores = ['store1', 'store2']

// function does logic if they are both finished loading
function initData() {
    var loaded = true;
    Ext.each(myComboStores, function(storeId) {
        var store = Ext.getStore(storeId);
        if (store.isLoading()) {
            loaded = false;
        }
    });
    if(loaded) {
        // do stuff with the data
    }
}

var allStores = [store1, store2],
    len = allStores.length,
    loadedStores = 0,
    i = 0;

for (; i < len; ++i) {
    allStores[i].on('load', check, null, {single: true});
}

function check() {
    if (++loadedStores === len) {
        AllStoresLoaded();
    }
}

function AllStoresLoaded() {
    //Do Something
}

function storeLoadingHandler(justLoadedStore) {
    // I use some quick hacky flag, you can do it by your own way
    justLoadedStore.loaded = true;

    var allStoresLoaded = true;

    // just walk through all stores registered in the application
    // do not forget to use MVC-style stores or add 'storeId' manually
    // or register every store with your custom code
    Ext.StoreManager.each(function(existingStore) {
        // we have to ignore system stores
        if (existingStore.storeId != 'ext-empty-store') {
            if (!existingStore.loaded) { // our flag or undefined
                // nope, at least one of stores is not loaded
                allStoresLoaded = false;

                return false
            }
        }
    })

    if (allStoresLoaded) // then do something
        alert('All stores are loaded.');
}

// add the loading handler for all stores
Ext.StoreManager.each(function() {
    this.on('load', storeLoadingHandler);
})

Ext.create("Ext.data.Store", {
    ...,
    loading: true,
    ...
});

function createStore(id) {
    return Ext.create('Ext.data.Store', {
        storeId: 'store_' + id,
        alias: 'store.store_' + id,
        proxy: {
            type: 'ajax',
            url: 'data.json',
            timeout: 300000,
            reader: {
                type: 'json',
                rootProperty: 'data'
            }
        }
    });
}

var storeArry = [],
    store = '';

for (var key = 0; key < 5; key++) {
    storeArry.push(createStore(key).storeId);
}

Ext.getBody().mask('Please wait..');
Ext.defer(function () {
    Ext.getBody().unmask();
    Ext.Array.forEach(storeArry, function (storeId) {
        //For checking store is created or not
        //if store is not created we can create dyanamically using passing storeId/alias
        store = Ext.getStore(storeId);
        if (Ext.isDefined(store) == false) {
            store = Ext.create(storeId);
        }
        store.load({
            callback: function () {
                //On every store call back we can remove data from storeArray or maintain a veribale for checking.
                Ext.Array.remove(storeArry, this.storeId);
                if (storeArry.length == 0) {
                    Ext.Msg.alert('Success', 'All stored is loaded..!');
                }
            }
        });
    });
}, 3000);