in operator does not narrow string type to index object

[deser]

Example:

const meow: string = 'domain1'

const hosts = {
    "domain1": {color: 'red'},
    "domain2": {color: 'blue'},
}

if(meow in hosts) {
   hosts[meow]
}

Playground:
https://www.typescriptlang.org/play?#code/MYewdgzgLgBAtgUxAdwFw2gJwJZgOYwC8MA5ACYhwCGuAjCQFAOiSwAWI0ERMA3gzEEwARBWp1h6XqAA2ITOhKYEZEgF8ANAKGjKNMACZJfWfMUAjGQFcE6rWqbYAZgApEKGLhgcuASj7a3pxQEADa7sgAugwOQA

Expected behavior:
meow can be used to index hosts if verification with in operator is done.

[torcoste]

This will work as you would expect if you do not forcibly set the type for meow

const meow = 'domain1'

const hosts = {
    "domain1": {color: 'red'},
    "domain2": {color: 'blue'},
};

if(meow in hosts) {
   hosts[meow]
}

Playground

[jcalz]

You forgot fill out the issue template completely.

This is working as intended. Non-union types are not narrowed upon assignment. Duplicate of or strongly related to #16976 Edit: I missed the point here, the ask is not that meow be narrowed to "domain1", but that it presumably should be narrowed to keyof typeof hosts.

This is a duplicate of #43284

[fatcerberus]

Assuming this worked (allowing arbitrary strings as indexers after an in check), objects can legally have extra properties thanks to structural subtyping—so what is the type of hosts[meow] then?

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.