JAVASCRIPT

change elements class javascript

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

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

if ( document.getElementById("MyElement").classList.contains('MyClass') )
{
document.getElementById("MyElement").classList.toggle('MyClass');
}

javascript change element class

//Overwrite all classes
element.className = "class";

//Add class
element.classList.add("class");

javascript change class name

function switchMode(){
    
    // Body switching
    if(document.getElementById("page-body").className == "page-body-day"){
        document.getElementById("page-body").className = "page-body-night";
    }else{
        document.getElementById("page-body").className = "page-body-day";
    }

    // Heading switching
    if(document.getElementById("main-heading").className == "main-heading-day"){
        document.getElementById("main-heading").className = "main-heading-night";
    }else{
        document.getElementById("main-heading").className = "main-heading-day";
    }

}

change class js

let containsClass = element.classList.contains('my-class');
element.classList.toggle('my-class', !containsClass);