ExtJs 5.0 : forEach on Array of Objects not working in IE8

I've a simple model -

Ext.define('MyModel', {
    extend: 'Ext.data.Model',

    requires: [
        'Ext.data.field.String'
    ],

    fields: [
        {
            type: 'string',
            name: 'currentA'
        },
        {
            type: 'string',
            name: 'currentB'
        },
        {
            name: 'A'
        },
        {
            name: 'B'
        }
    ]
});

Here is some operation that I'm doing on the data for that model-

 onBeforeRender: function(component, eOpts) {
    var mystore = Ext.getStore('Mystore');
    mystore.load({
        callback: function(){
            var entity = headerStore.getAt(0);
            var bs = entity.data.B;
            var as = entity.data.A;
            var currentB = entity.data.currentB;
            var currentA = entity.data.currentA;

            bs.forEach(function(record) {
                // do some operations
            });
            as.forEach(function(record) {
                // do some other operations
            });
        }
    });
}

Now, when iterating over variable "bs", which is clearly an array of objects, IE 8 complains

"Object doesn't support this property or method"

for the forEach function. This works fine in Chrome.

Here is the json for the model -

{
  "currentA": "a",
  "currentB": "b",
  "A": [
    {
      "name": "a",
      "id": 1
    }
  ],
  "B": [
    {
      "name": "b",
      "id": 2
    }
  ]
}

Why is IE not able identify it as an array?