This error message on Google Chrome console: Specification mandate value for attribute async That would happen if we generated XML page which acted as HTML , or XHTML . And we forgot to define the value for a particular HTML element attribute. In this case, the value for async attribute (in script element). The "async" Attribute Strictly Needs Value in XHTML Earlier, it was like this: <script type="application/javascript" src="URL_SOURCE" async></script> And the XHTML page wouldn't be rendered. It was just blank, but still with the XML attached (if we view the page source/inspect element). Solution To fix that, put the value for that attribute. We can put async , 1 , or true for that. Use async : <script type="application/javascript" src="URL_SOURCE" async="async"></script> Or use 1 : <script type="application/javascript...