How to integrate a html bootstrap code into a javascript code?

I wrote a html website. There is a button created with bootstrap. I want to change the design of the button and the label text on it, depending on a boolean variable.

Here are the two types of buttons:

<div class="alert alert-success" role="alert">
    <center><strong>Open</strong></center>
</div>

<div class="alert alert-danger" role="alert">
    <center><strong>Close</strong></center>
</div>

How can I integrate this html buttons in this javascript code?:

    <script>
    var open = true;

    if (open = true) {


    } else {

    }

</script>

Thanks for your help!