handbook | A gentle introduction to the art of Nodejitsu | Runtime Evironment library

I have been self-learning TypeScript via the TS docs. While reading a section that I posted below, (in text form, as well as the link), I came across a word I haven't heard before ARITY. Usually I just search the TS docs to find out what some specific syntax means, but I am guessing this isn't TypeScript, because the docs didn't return any specific definition for 'Arity' in the search Results. As stated above, below is the documentation I came across, that uses 'Arity'. The documentation relies on heavily on the definition of 'arity', and I couldn't find anyone defining it here on stackoverflow, or in a DDG search. If anyone could define this for me that would be awesome.

The turbo handbook explains target: '_top' here and here.

But I still don't understand what's the difference between these two forms:

#1

The following code

I am trying to implement controlling executability of ReactiveUI command according to this guide: guide.
But I am getting an exception: "Operation is not valid due to the current state of the object."
How should I fix that?
My code sample:

When asserting that a field is definitely initialized in a class, what’s the difference between ! (exclamation point, definite assignment assertion) and the declare modifier?

The following code is an error in strict mode since TS doesn’t know for sure that the field has been initialized.

I would like to create a type that only allows properties that start with a given prefix like that:

I'm currenlty teaching myself python for data science and stumbled upon a chapter that I have been looking at for hours but I don't understand. I hope you can help me understand it. In the example they want to code the k-nearest neighbors. The code looks like this:

According to this link, I am using jitsi Android SDK

BroadcastEvent is undefined in jitsi Android SDK sample

I want to create a Typescript Type for an array of objects. In this array of objects, I require only one object to have a property set to true.

You can probably solve it just with this typescript example, but I will provide a long and detailed explanation.

Let's say (just an example!) I want to recreate a tag (or a dropdown list). My custom select has two have at least two options and I always want to have only one object to be active. I have three models: abstract class SimpleDropDownListElement { constructor(public label: string, public value: any) {} } class DropdownListElement extends SimpleDropDownListElement { constructor(public label: string, public value: any, public active?: false) { super(label, value); } } class DropdownActiveListElement extends SimpleDropDownListElement { active = true; constructor(public label: string, public value: any) { super(label, value); } } I want to have an array with at least one (or more) DropdownListElement(s) and one (always one - e.g. never 0 or 2+) DropdownActiveListElement. Any order (object with active set to true can be everywhere in the array). So my idea was to create a type like this: type DropDownOptionsArray = [DropdownActiveListElement, DropdownListElement, ...Array]; And that works, however, I need to have the object with the active property set to true as the first element of my array. So my idea was to reverse the array (not very smart), but I still get problems if the array holds more than 3 values. type Reverse = Tuple extends [infer A, ...infer B]? [...Reverse, A] : []; const dropInvertedWithInvertedType: Reverse = [new DropdownListElement('b', 'b'), new DropdownActiveListElement('a', 'a')]; const dropInvertedWithInvertedType1: Reverse = [new DropdownListElement('b', 'b'), new DropdownActiveListElement('a', 'a'), new DropdownListElement('b', 'b')]; // errors Then I started to go crazy with rest elements (hoping for TS v4 to help me with some magic): type DropDownOptionsArray = [...[DropdownActiveListElement], ...Array, ...Array]; // OK const twoEntries: DropDownOptionsArray = [new DropdownActiveListElement('a', 'a'), new DropdownListElement('b', 'b')]; const fourEntries: DropDownOptionsArray = [new DropdownActiveListElement('a', 'a'), new DropdownListElement('b', 'b'), new DropdownListElement('b', 'b'), new DropdownListElement('b', 'b')]; // should not error - but errors const twoEntriesRandomPos: DropDownOptionsArray = [new DropdownListElement('b', 'b'), new DropdownActiveListElement('a', 'a'), new DropdownListElement('b', 'b')]; const twoEntriesRandomPos: DropDownOptionsArray = [new DropdownListElement('b', 'b'), new DropdownListElement('b', 'b'), new DropdownActiveListElement('a', 'a')]; // should error const twoActiveEntries: DropDownOptionsArray = [new DropdownActiveListElement('a', 'a'), new DropdownListElement('b', 'b'), new DropdownActiveListElement('a', 'a')]; const noActiveEntry : DropDownOptionsArray = [new DropdownListElement('b', 'b')]; // should have a different error Writing overloads verbosely is not feasible, we could have an array of 20+ elements. To summarize, I would need this Type: array of objects holds at least two or more objects only one object has to have property active = true (all other objects may have active = false) the object with property active = true can be placed at any index in the array (from index 0 to index array.length - 1 ) Thank you!!