DOM Manipulating a list of CSS classes Removing a class

Removing one class from an element requires a bit of manipulation of the className property.

var toRemove = "bar",
  el = document.getElementById("link1");
el.className = el.className.replace(new RegExp("\\b" + toRemove + "\\b", "g"), "").trim();

Removing multiple class names would require a loop. The remaining examples will use a function to isolate the work

function removeClass(el, name) {
  name = name.split(/\s+/);
  var index = name.length,
    classes = el.className;
  while (index--) {
    classes = classes.replace(new RegExp("\\b" + name[index] + "\\b", "g"), "").trim();
  }
  el.className = classes;
}
var el = document.getElementById("link1");
removeClass(el, "bar baz");

Multiple elements with multiple class names to remove would require two loops

function removeClass(els, name) {
  name = name.split(/\s+/);
  var regex, len,
    index = name.length;
  while (index--) {
    regex = new RegExp("\\b" + name[index] + "\\b", "g");
    len = els.length;
    while (len--) {
      els[len].className = els[len].className.replace(regex, "").trim();
    }
  }
}
var els = document.getElementsByTagName("a");
removeClass(els, "bar baz");

A single class name may be removed as a string. To remove multiple class names, use ES6's spread operator:

document.querySelector("#link1").classList.remove("foo");
document.querySelector("#link2").classList.remove(...['foo', 'bar']);

For multiple elements, you'll need to remove the class names inside of a loop

document.querySelectorAll(".foo").forEach(el => {
  el.classList.remove(...['bar', 'baz']);
});