Javascript variable statement as key value pair

Question

I´m programing in javascript using Relay and I´ve found the following statement:

const { connectionType: UsersConnectionType } = connectionDefinitions( { nodeType: UserType });

What does exactly the { connectionType: CustomerConnectionType } means ? How to reference that variable later and how to export it if I have two more of those varibles, like:

const { connectionType: CustomerConnectionType } = connectionDefinitions( { nodeType: CustomerType });
const { connectionType: ItemConnectionType } = connectionDefinitions( { nodeType: ItemType });

Answer 1

I think I just found it - it's a Destructuring assignment. There's also other forms of it with arrays, etc. It's an ECMAScript 6 thing.

A property can be unpacked from an object and assigned to a variable with a different name than the object property.

var o = {p: 42, q: true};
var {p: foo, q: bar} = o;

console.log(foo); // 42 
console.log(bar); // true

Frankly I think the syntax is confusing - I would have used var { foo: p, bar: q} instead (or a completely different syntax entirely, so it doesn't look confusingly similar to an object initialization), but I suppose they had their reasons.

In your case the line

const { connectionType: UsersConnectionType } = connectionDefinitions({nodeType:UserType});

is actually the equivalent of

const UsersConnectionType = connectionDefinitions({nodeType:UserType}).connectionType;

just with more bling and confusion. :)

Answer 2

it is a way to initialise UsersConnectionType take a look at the example

function A(){
    return {x : 5};
}

let {x : y} = A();

console.log(y);

incase you know what the return value of the function is, you can initialise them this way .

{x : y} 

here y gets assigned the value of x returned from the function A()