How can I call a javascript function from a HTML file

Usually I use:
< script> functionName.(); < /script>
But that doesn’t work.

What are you trying to do exactly? You should write code in scripts not in HTML files.

I think this will be very helpful to you

This makes using html in your project very easy. This example shows how you can bind a click event to a button in html-handler.js and will give you a good idea how you can integrate interactions between your html and javascript

In a nutshell, the CSS ins’t being added correctly for introjs. I’ve also called introJs().start() after the HTML and CSS has been added in ui.js to ensure that it is being called at the right time.

The link that @Ryynosaur gives the example of how CSS should be added via Javascript.

Here is a fork of the project that shows the introJs popup: