Checks whether the value of the field has changed since the last time it was checked.
If the value has changed, it:

1. Fires the {@link #change change event},
2. Performs validation if the {@link #validateOnChange} config is enabled, firing the
{@link #validitychange validitychange event} if the validity has changed, and
3. Checks the {@link #isDirty dirty state} of the field and fires the {@link #dirtychange dirtychange event}
if it has changed.
function() {
        if (!this.suspendCheckChange) {
            var me = this,
                newVal = me.getValue(),
                oldVal = me.lastValue;
            if (!me.isEqual(newVal, oldVal) && !me.isDestroyed) {
                me.lastValue = newVal;
                me.fireEvent('change', me, newVal, oldVal);
                me.onChange(newVal, oldVal);
            }
        }
    }