toggle checkbox with javascript

I want to uncheck a checkbox using javascript. I have one button which just unchecks the box and works fine:

function clear() {
document.getElementById("check").checked = "";
}

I have another button that I want to check the box if not checked and uncheck if it is. Below doesn't uncheck the box. I can can switch the if statement and does works the opposite way. What's the problem?

function switch() {
if (document.getElementById("check").checked !== "checked") {
  document.getElementById("check").checked = "checked";
} else {
  document.getElementById("check").checked = "";
}

Thanks!