I have merge recently css and js from magento backend. after this backend menu not work i got following error.

Uncaught TypeError: Cannot read property 'length' of undefined

I dont know what is problem with this.

  • You have to check manually which JS causes conflict..First disable custom modules and enable one by one. Commented Dec 26, 2016 at 5:38

1 Answer 1


make sure you have load prototype.js before jquery-your-version.js . you will find this in your main.xml

<block type="adminhtml/page" name="root" output="toHtml" template="page.phtml">
           <block type="adminhtml/page_head" name="head" as="head" template="page/head.phtml">
                <action method="setTitle" translate="title"><title>Magento Admin</title></action>
                <action method="addJs"><script>prototype/prototype.js</script></action>
                <action method="addItem"><type>js</type><name>js/jquery.js</name><params/><if/><condition>can_load_ext_js</condition></action>

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