This is generally done through an identity function. This will allow you to constrain your inputs while still using their specific types like this ([demo in ts playground][1]):

```ts
function defineSites<T extends Record<string, ISiteDetails>>(template: T) {
    return template;
}

const sites = defineSites({
    stackoverflow: {url: 'https://stackoverflow.com/'},
    google: {url: 'https://www.google.com/'},
    azure: {url: 'https://portal.azure.com/'}
})
```
I have a little one-liner that I import sometimes. It's **higher order identity**.

```ts
export const HOI = <Constraint> () => <T extends Constraint> (definition: T) => definition;

export const defineSites = HOI<Record<string, ISiteDetails>>();
// use as normal
```
You may wish to write this as a function if you need it in a `.tsx` file
```ts
export function HOI<Constraint>() { 
    return () => <T extends Constraint> (definition: T) => definition;
}
```

[1]: https://www.typescriptlang.org/play?#code/GYVwdgxgLglg9mABAEwKbBmVBlGVUDOAPACqKoAe+YyBiASqhHAE7JEFQuYDmANIgCSufABFUUAIYwANgQB88gBT4AtgAcZk-AC5EJAJSIA3gChEFxCwkgWSNZu2oA3KYC+p05nwtgkiKhCIqjiUrJ0ZpaItjJ6nNxgPK4epsxgnIgEeISIALwo6Jg42QRKkZac-gDWcABuqL4ycADuesYxegDkABZQUOoEOgD0Q5UQNfWNLQB0zKpDnW585pY8cHA8MqhtHYg9fQPDQ80n02sbW7Nw84vLUZIAXrbbJrv7-YMj6qxSMtOPzyuNw8bgMnigAE91IFggA5SSqHL5KqoCFwYCISHQ9GZErORAjRAAIjGEwawCazSJiAAPsTzptUNS6USAdYiZ5CQRunAQDJkIhmqwqqkEBl8JxggBxdbIPRwhFIvakurkymdTlDTI8vkCvyyUXpKCYwhQYIAIUkcsQCsRdHynUoCM0qE6QA

I have an object like this ([demo in ts playground][1]):

```js
const sites = {
    stack: {url: 'https://stackoverflow.com/'},
    google: {url: 'https://www.google.com/'},
    azure: {url: 'https://portal.azure.com/'}
} as const
```

What I'd like to do is create a union type with all the keys that were used, which I can do like this:

```js
type SiteNames = keyof typeof sites; // "stack" | "google" | "azure"
```

However, I'd also like to add type saftey to the `sites` intialization where all of the object values are of a certain type like this ([demo in ts playground][2]):

```js
interface ISiteDetails {
    url: string;
}

const sites: Record<string, ISiteDetails> = {
    stackoverflow: {url: 'https://stackoverflow.com/'},
    google: {url: 'https://www.google.com/'},
    azure: {url: 'https://portal.azure.com/'}
} as const
```

This provides some type checking when creating `sites`, but also removes the [**const assertion**][4] from the final type, so now SiteNames just resolves to a string:

```js
type SiteNames = keyof typeof sites; // string
```

**Question**: Is there any way to have both?  Strong typing when creating a `Record<any, ISiteDetails` but also the ability to extract all the object keys into a new union type?

**Workaround**: not as ergonomic, but I could add a final layer of type checking by reassigning site to an exported variable like this ([demo in ts playground][3]):

```js
const SitesTyped: Record<SiteNames, ISiteDetails> = sites;
```

[1]: https://www.typescriptlang.org/play?#code/JYOwLgpgTgZghgYwgAgJIGViQCITHYAGwGdkBvAKGWuQFcpCAuZYsKUAcwG4KBfCiggD2IViywRSAXnJUarRAGshAN2gxCQgO7My9JsgDkACzBgADsUYB6awoTK1sTVoB0wgLbXDvADRzqDiEhDkIIXX1mEzNLG2stBNcgkLD3IS8ffxpkOAAvenDySKNTCytbcyEofEJXPIK0jP5eHNJhUTABCjAAT3MUTEgAOTgPSWQZRQgeoRhkXv7Z8UhiLmRbZAAie0d1F03kAB8t5NCIA+PN+qhzgQ3iYyFaQgATZC0qxUERMRWwQYgAHFgi9mACRmNpEYdqo9tpDHdrCxHs83vAiN8OvNJP8JAAhOCg5Dg0bjGSGCAAD1G5jChiAA
[2]: https://www.typescriptlang.org/play?ssl=12&ssc=47&pln=13&pc=1#code/JYOwLgpgTgZghgYwgAgJIGViQCITHYAGwGdkBvAKGWuQFcpCAuZYsKUAcwG4KBfCiggD2IViywRizAEoRhUACYAeVuxAcANGkw48BEgD5kAXnJUarRAGshAN2gxCQgO7My9JsgDkACzBgABykAemDLBBt7WCdnADphAFtgr14Nc2oOISEOQgg3D2ZffyDGUOdy2Mzs3PihJJS0mmQ4AC96PPIC7z9AkOCAoSh8QljW9tr6-l5m0mFRMAEKMABPAJQdCAA5OATJE2QrCGWhGGQVtZPxSGIuZFCWNk4Be+IfIVpCBWRnQatBETE1zAGwA4lkFMwNttdqRTF5wpEHDEvM9giw3h8vvAiP95mdJMCJAAhOAQ5BQnZ7OEQAAeOwCuS8QA
[3]: https://www.typescriptlang.org/play?ssl=13&ssc=59&pln=13&pc=1#code/JYOwLgpgTgZghgYwgAgJIGViQCITHYAGwGdkBvAKGWuQFcpCAuZYsKUAcwG4KBfCiggD2IViywRSAXnJUarRAGshAN2gxCQgO7My9JsgDkACzBgADsUYB6awoTK1sTVoB0wgLbXDvADRzqDiEhDkIIXX1mEzNLG2stBNcgkLD3IS8ffxpkOAAvenDySKNTCytbcyEofEJXPIK0jP5eHNJhUTABCjAAT3MUTEgAOTgPSWQZRQgeoRhkXv7Z8UhiLmRbZAAie0d1F03kAB8t5NCIA+PN+qhzwRExQckAFT6IABNmACUIYSg3gB5HiMxsRfGhHrh8ERiAA+CbLSQ8CgbYjGIS0QhvZBaKqKO4deaSMCPADiwQ+yCBo3GMkMO1Ue20hgEKLRGKx8CI+LEK2JEgAQnAKVSQfDDBAAB6jcxhQxAA
[4]: https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-4.html#const-assertions