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
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
function foo(x: number, y: string = "default", z?: number) {
// ...
}
foo(42);
