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Access Array with String key

I have two variables with JSON files. The first is a list of keys looks like this:
keylist = ["key1","key2","key3"]
The second one is generated from a database and looks like this:
data = {
"key1"{
#further data
},
"key2"{
#further data
},
"key3"{
#further data
}
}
Now I want to access the second element of the database with the key from the keylist
data.keylist[1];
Which doesn't work because the return of keylist[1] is a String? I did some research and the use of the window function was proposed. So I tried this:
window["data." + keylist[1]]();
Which leads to a "is not a function" error. What can I do to solve this problem?

As simple as that:
const mydata = data[ keylist[1] ];
Also, your code is correct from the point of syntax, but it tells completely different than you expect it to tell.
data.keylist[1];
tells JS that you expect to have an object called data which has a property called keylist and which is (most likely) type of array, and you want to get the second element of this array.
PS: And one more point here. Your question title is not completely correct because of the difference between Arrays and Object in JS.
There is no "string keys" for arrays in JS, so you cannot "access array with a string key". Well, truly speaking there are, but not for items of array. Array items only have numeric index, which you can use to access it. Objects, in contrast to arrays, may have named properties. So when you see something like that: data = myVar['data'], you can tell that you're dealing with an object, while data = someVar[0] can be both, an Array (most likely) or also an Object with key named '0'.

I don't think the issue you're having with your first example is because it returns a key. I believe the issue is because data doesn't have a property called keylist. Instead of that, try it as
data[keylist[1]]
and see if that works for you. The reason this one should work is that, in this situation, Javascript will evaluate the string return of keylist[1] and then use it as a string index for the data variable. Let me know if this works out for you :D

You can try using using something like this.
data[keylist[1]]

How do I access the 'str' value in my object?

I am trying to return the value under the key 'str' in an Object but I am having trouble accessing the value.
This is what is returned in the console:
Currently I am using a map function to go over the array and just return the _str value like so:
let idx = currentArray.map(function(x) {
return x._id._str;
});
However it is still returning the value as an object. How can I get just the value of the _str key?
Here is the full array without specifying the id field. This is what is returned if you jsut return 'x' in the map function.

You've clarified that the screenshot is of x._id. So to access _str, you'd use x._id[0]._str: The _str property is in the object referenced by the 0 property (the first entry in the array x._id refers to).
Note that in general, _-prefixed properties are meant not to be accessed by code outside the code responsible for the objects in question. You don't seem to be responsible for them, so accessing those properties is likely to make your code rely on undocumented properties that may change in the next "dot" release of whatever lib you're using. It's just convention, but it's a very common convention.

If you right click on the property, most browser consoles offer the ability to copy property path.

Based on this SO post and the docs, it appears that you can probably use x._id.str.

If I understand correctly, you are receiving the str value but it is an object instead of the string literal. In other words, you are getting _str: "598..." instead of "598....". A possible solution would be to use the mongo javascript function to convert the str value to a string.
In your case, I think something like return x._id.str; may work as _id is a MongoID.ObjectID.
I've also linked the documentation below for reference.
https://docs.mongodb.com/manual/reference/method/ObjectId/
Here's a relevant SO answer as well: Convert ObjectID (Mongodb) to String in JavaScript

I think you should write x[_id]._str because _id is one of the array objects.

Accessing response data using Angular.js with numerical named field

My response object has a field called "50", so right now I'm trying to access and save that data doing something like this:
var thing = $scope.data.array[0].50;
However I'm getting an error on the console when I simply reload the page with the function not even running. When I get rid of the 50, everything is fine. There is indeed a field called "50" inside the $scope.data.array[0] and I do not have access to change the response. Is there something wrong with this because the field is called "50" and maybe JS is interrupting that as a number instead??
Also when I changed "50" to something random like "af", then I get no errors on refresh.
this doesn't work
var thing = $scope.data.array[0].50;
this works
var thing = $scope.data.array[0].af;

The following should work if your first element of the array has a property called "50".
var thing = $scope.data.array[0]["50"];
Property accessors provide access to an object's properties by using the dot notation or the bracket notation.
Syntax
object.property
object["property"]
JavaScript objects are also associative arrays (hashes). Using these you can associate a key string with a value string as shown in the example above.
The reason as to why you don't get an error when accessing $scope.data.array[0].af; is because "af" is valid identifier for a property. Dot notation only works with property names that are valid identifiers. An identifier must start with a letter, $, _ or unicode escape sequence.
For all other property names, you must use bracket notation.

Javascript: Using a string to acces objects property

If I have a string like
var s = someString;
But I do NOT know the value of that string, since the program obtains it from external file, and I wanted to use that string to access an objects property, like:
alert(obj.s)
//or
alert(obj[s]);
How would I do that? The code I wrote doesn't work, the alerts are just empty (and I'm positive that s is NOT empty AND that there is a property with the same value as s). But when I try to access an object normally it works fine (using a property name I already know):
alert(obj.name);
//or
alert(obj["name"]);
So...any ideas? Thanks

javascript object instantiation to include an array as one of the properties

I am trying to create an object which includes an array stPoints as one of its properties.
I am getting an error message saying that stPoints is undefined. What is the proper way to declare an array property within an object?
this is my code:
var temp={stName:"#states.stateid#",stPoints:[]};

This is correct. You must be referencing it incorrectly.
temp.stPoints

var temp={
'stName':"#states.stateid#",
'stPoints':[]
};
However, if the property name is a valid javascript identifier, as in this case, you should not have problem.