使用 javascript 将 class 添加到 div 元素

Question

im really new to js, and im currently making a webiste. Because i have a repeated html code for the header and footer of the wepage, i used php to call the html file rather than repeating the same code. On the other hand,i wanted the current active page to have a different color, therefor i am using javascript to get the name of the class and add the class active to make a exeption in css. getting the id seems to be working, but i cant find the class active being add. why is this?

<p class="activepage" id="felt">aegearg<p>    
<script>
      var element = document.getElementsByClassName("activepage")[0];
      var id = element.id;
      getElementsByClassName(id).classList.add("active");
    </script>

Answer 1

ids of the elements should be unique, search your element by id and then remove or add the desired class name

document.getElementById("MyElement").classList.add('MyClass');

document.getElementById("MyElement").classList.remove('MyClass');

Answer 2

you can use this code:

document.getElementById("IdElement").classList.add("ClassNameAdd");

Answer 3

you can do it like that:

const element = document.QuerySelector("#activepage");
element.ClassList.add("active");

Answer 4

In jQuery

$('#activepage').addClass('active');

instead of addClass you can toggleClass for removing and adding class