How to override a templates default option with javascript and css

Question

I´m using a template built upon bootstrap. It has a sidebar menu which can be toggled clicking on a button with the following code:

<a href="javascript:;" class="menu-toggler responsive-toggler" data-toggle="collapse" data-target=".navbar-collapse">

The menu's default state is uncollapsed. I know the following are very simple questions, but I have almost zero experience with javascript and css, and have not found a way to do it:

How can I call the previous code's functionality upon page load?

And what exactly is href="javascript:;" calling? How does it work?

Thank you.

Answer 1

For a more accurate answer, please provide a link to the template.

How can I call the previous code's functionality upon page load?

Try to simulate a click of the link on page load, with something like

 document.querySelector('.menu-toggler.responsive-toggler').click();

And what exactly is href="javascript:;" calling? How does it work?

Apparently, it call javascript code from a link, but I have to say I have never this syntax before. In this particuliar case, it cancels the basic anchor functionnality to go to another webpage or id in the page.