Conditional Branching

if (condition) statement1 else statement2 runs the first statement when the condition is truthy, otherwise the optional else part; group several statements in {...}. switch evaluates its expression once and jumps to the first case that is strictly equal (===), then runs until break or return; without break it falls through into the next case. To choose a value, use a ? b : c, || or ?? (Truthiness).

switch, the conditional operator and the dangling elseJavaScriptLive

const label = (code) => {
  switch (code) {                   // compared with ===, so "404" never matches 404
    case 301:
    case 302: return "redirect";    // stacked cases share one body
    case 404: return "not found";
    default: return code >= 500 ? "server error" : "other";
  }
};
const age = 10;
if (age > 18) if (age > 65) console.log("senior"); else console.log("adult"); // no output
console.log(label(503), label(302), label("404"), age >= 18 ? "adult" : "minor");

server error redirect other minor

The nested if prints nothing because an else belongs to the nearest if. Use braces, and wrap a case body in { } when it declares variables: all cases share one scope.

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Conditional Branching