Object destructuring solution for long arrays?

But what if the array has 100 items and I want the 99'th age ?

Arrays are objects, so this will do:

let {title: lectureTitle, topics: {98: {age: thirdAge}}} = lecture;

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Note however that the [...] type of destructuring works with any iterable, whereas {...} only works with objects (and therefore arrays). For the above solution to work with arbitrary iterables you will have to spread the iterable and wrap it with an array.

let {title: lectureTitle, topics: {98: {age: thirdAge}}} = [...lecture];

Probably too late to reply this,

const index = 65
const {title: lectureTitle, topics: {[index]: {age: thirdAge}}} = lecture

because in real life we normally would be using dynamic indices for arrays to destructure, square brackets instead of numbers or just { index: {age}} doesn't work.