Are you sure?

Your C# example:

var output = input switch
{
    null    => "Null",
    0       => "Zero",
    > 0     => "Positive",
    _       => "Negative"
};

JS proposal for match:

const output = match input {
    when null:    "Null";
    when 0:       "Zero";
    if input > 0: "Positive";
    default:      "Negative";
}

Pretty sure they meant match as in pattern matching, not switch as in switch/case/break.

You can see the proposal here: https://github.com/tc39/proposal-pattern-matching