unicorn/prefer-default-parameters

A fallback written as name = name || "stranger" is hidden in the function body. A default parameter puts it in the signature, where callers and editors can see it.

The rule reports ||, ??, ||= and ??= when the fallback is a literal and the parameter is the last one. It reports nothing if an earlier statement in the function could have a side effect, such as a function call.

Configure

Off by default. To turn it on:

[lint.rules]
"unicorn/prefer-default-parameters" = "error" # or "warn"

Examples

Reported:

function greet(name) {
  name = name || "stranger";
  return `Hello, ${name}`;
}

function connect(host, port) {
  const actualPort = port ?? 8080;
  return open(host, actualPort);
}

Not reported:

function greet(name = "stranger") {
  return `Hello, ${name}`;
}

function connect(host, port = 8080) {
  return open(host, port);
}

A parameter that isn't the last one and a fallback that isn't a literal are left alone:

function connect(host, port) {
  host = host || "localhost";
  port = port || defaultPort();
  return open(host, port);
}

When not to use it

A default parameter only applies to undefined. || also replaces 0, "", false and null, and ?? also replaces null. If callers pass those values and rely on the fallback, keep the reassignment.