rspec/rules/S4623/javascript/rule.adoc

== Why is this an issue?

Unlike in JavaScript, where every parameter can be omitted, in TypeScript you need to explicitly declare this in the function signature. Either you add ``++?++`` in the parameter declaration and ``++undefined++`` will be automatically applied to this parameter. Or you add an initializer with a default value in the parameter declaration. In the latter case, when passing ``++undefined++`` for such parameter, default value will be applied as well. So it's better to avoid passing ``++undefined++`` value to an optional or default parameter because it creates more confusion than it brings clarity. Note, that this rule is only applied to the last arguments in function call.


=== Noncompliant code example

[source,javascript]
----
function foo(x: number, y: string = "default", z?: number) {
  // ...
}

foo(42, undefined); // Noncompliant
foo(42, undefined, undefined); // Noncompliant
foo(42, undefined, 5); // OK, there is no other way to force default value for second parameter
----


=== Compliant solution

[source,javascript]
----
function foo(x: number, y: string = "default", z?: number) {
  // ...
}

foo(42);
----


ifdef::env-github,rspecator-view[]

'''
== Implementation Specification
(visible only on this page)

=== Message

Remove this redundant "undefined".


=== Highlighting

"undefined"


endif::env-github,rspecator-view[]