Disable a extjs xtype button bases on a javascript variable value

I have a button which I need to be disabled if the javascript variable is 'user'. I am not sure how to go about it. This is what I tried :

var loggedin_role = '<?php echo "$user_role"; ?>';          

                 xtype: 'button',
                if(loggedin_role =='user') {
                    disabled:true
                },
                text: 'Save',

Using PHP

You can do it using simple php logic.

<?php if ($user_role=='user'): ?>
disabled: true;
<?php endif; ?>

Using ExtJS event

You can use any event handlers. activate( Ext.Component this, Object eOpts )

var loggedin_role = '<?php echo "$user_role"; ?>';          

        xtype: 'button',
        listeners : {
            activeate: function(btn, eOpts){
                if(loggedin_role =='user') {
                    btn.disable();
                }
            }
        },