Often when using jQuery and you aim to add or remove a class based on a state variable, you will see a function such as.

function updateInterface () {
    var shouldShowLogout = user.isLoggedIn;

    if (shouldShowLogout)
        $('.logout-button').addClass('active');
    } else {
        $('.logout-button').removeClass('active');
    }
 } 

This function is hard to read and basically repeats itself in the if and else clauses. The function implementation can be refactored down to 2 lines using a ternary if operator.

function updateInterface () {
    var shouldShowLogout = user.isLoggedIn;
    $('.logout-button')[ shouldShowLogout ? 'addClass' : 'removeClass' ]('active');
}

Since you can access functions of a an object in JavaScript like values, you can use the [] accessor to return the correct function based on the ternary if statement and them immediately call it using (), or in this case passing our class name value ('active').

You could even take this down to a single line.

function updateInterface () {
    $('.logout-button')[ user.isLoggedIn ? 'addClass' : 'removeClass' ]('active');
}

Although this final single line approach may be confusing to the next developer who is not already familiar with the pattern.