If I am accessing an index of an array based on a variable, I would first want to check that the index exists.

My understanding is that if I try to access an index outside of the array's range, I will get a value of 'undefined.' So,

(typeof array[i] === 'undefined')

should return true if array[i] does not exist.

Would it also be possible, because undefined is falsey, to get the same result with

!array[i]

?

Edit: Thanks for the help!

To clarify I am referring to the first question mark, array?.length. I saw this somewhere and can't recall what it does.

const array = [1,2,3]

array?.length > 0 ? 'Array contains elements' : 'No elements within array';

Specifically, I want to use the syntax if(arr.length) instead of if(arr.length > 0).

Here's an example of it in function for an Object I'm working on:

name(optStr){ return (arguments.length ? (this._name = optStr) : this._name); } (does set/get)

Edit: I went with this as a general get-set:

field(field, value){
    if(value === undefined)
        return this[field];
    if(Array.isArray(value))
        return this[field] = [...value];
    return this[field] = value;
}