Update an elements class definition by removing and adding classes

setClassList.js

/**
 * Remove and add classes to any element. Removes are performed before adds.
 * @param {string} Selector to target. Must resolve to a single element.
 * @param {string|array} Classes to add. If using single string, can only be a single class. Otherwise use array of strings for each class to add.
 * @param {string|array} Classes to remove. If using single string, can only be a single class. Otherwise use array of strings for each class to remove.
 */
function setClassList(selector, classesToAdd, classesToRemove) {
  let element = document.querySelector(selector);

  if (Array.isArray(classesToRemove) && classesToRemove.length > 0) {
    for (let i = 0; i < classesToRemove.length; i+= 1) {
      if (classesToRemove[i]) {
        element.classList.remove(classesToRemove[i]);
      }
    }
  } else if (classesToRemove) {
    element.classList.remove(classesToRemove);
  }
  if (Array.isArray(classesToAdd) && classesToAdd.length > 0) {
    for (let i = 0; i < classesToAdd.length; i+= 1) {
      if (classesToAdd[i]) {
        element.classList.add(classesToAdd[i]);
      }
    }
  } else if (classesToAdd) {
    element.classList.add(classesToAdd);
  }
}