Type 'keyof T' does not satisfy the constraint 'string'.

[juanjosegutierrez]

TypeScript Version: 3.0.0-dev.201xxxxx
Issue still happens on dev version.

Search Terms: keyof T

Code

I am getting this error in Typescript 2.9.

(106,55): Type 'keyof T' does not satisfy the constraint 'string'.
  Type 'string | number | symbol' is not assignable to type 'string'.
    Type 'number' is not assignable to type 'string'.

This is the line that deals with keyof T in the react router types index.d.ts

type Omit<T, K extends keyof T> = Pick<T, ({ [P in keyof T]: P } & { [P in K]: never } & { [x: string]: never, [x: number]: never })[keyof T]>;

Expected behavior:
When I used Typescript 2.8 this error did not show up. However, when I updated Typescript the error showed up. The react router types should work properly like in 2.8.

Actual behavior:
I am getting the error above.

Playground Link:
No link but I am using react router with Typescript.

Related Issues:
No related issues.

[j-oliveras]

Breaking change since 2.9: https://github.com/Microsoft/TypeScript/wiki/Breaking-Changes#keyof-now-includes-string-number-and-symbol-keys

[ackvf]

The only solution as of now is to use a flag and disable this new behaviour. Fixing the packages by hand is senseless.

tsconfig.json

"keyofStringsOnly": true

[ekilah]

I'm having this issue too, and I don't understand what's going on well enough to resolve it.

Most packages seem to have updated their typings to avoid this, including react-router. However, some dependencies seem to come with their own @types dependencies, as shown in my error case:

Failed to compile.

[at-loader] ./node_modules/@types/react-router-redux/node_modules/@types/react-router/index.d.ts:106:55 
    TS2344: Type 'keyof T' does not satisfy the constraint 'string'.
  Type 'string | number | symbol' is not assignable to type 'string'.
    Type 'number' is not assignable to type 'string'.

As you can see, the error is coming from react-router-redux's own @types dependency, which I was surprised existed in my project hierarchy to begin with...

react-router has updated their types for TS 2.9, however the typing file for react-router that is within react-router-redux in this error message (./node_modules/@types/react-router-redux/node_modules/@types/react-router/index.d.ts) does not have this update. I don't see a place in the react-router-redux package.json where I could try and fix this, so I'm not sure where this older version of the @types file is coming from. Does anyone know?

My project does not even directly depend on the @types/react-router it turns out, though I tried adding the updated version as a direct dependency to resolve this by adding "@types/react-router": "^4.0.27", to my "dependencies" list. That didn't work; I ended up with two entries in my yarn.lock:

"@types/react-router-dom@^4.0.8":
  version "4.2.6"
  resolved "https://registry.yarnpkg.com/@types/react-router-dom/-/react-router-dom-4.2.6.tgz#9f7eb3c0e6661a9607d878ff8675cc4ea95cd276"
  dependencies:
    "@types/history" "*"
    "@types/react" "*"
    "@types/react-router" "*"

"@types/react-router-redux@^5.0.15":
  version "5.0.15"
  resolved "https://registry.yarnpkg.com/@types/react-router-redux/-/react-router-redux-5.0.15.tgz#aebc593bd3426adb6ae2eba6ac8c919ee232ce7b"
  dependencies:
    "@types/history" "*"
    "@types/react" "*"
    "@types/react-router" "*"
    redux ">= 3.7.2"

"@types/react-router@*":
  version "4.0.23"
  resolved "https://registry.yarnpkg.com/@types/react-router/-/react-router-4.0.23.tgz#d0509dcbdb1c686aed8f3d5cb186f42e5fbe7c2a"
  dependencies:
    "@types/history" "*"
    "@types/react" "*"

"@types/react-router@^4.0.27":
  version "4.0.27"
  resolved "https://registry.yarnpkg.com/@types/react-router/-/react-router-4.0.27.tgz#553f54df7c4b09d6046b0201ce9b91c46b2940e3"
  dependencies:
    "@types/history" "*"
    "@types/react" "*"

Why would the "@types/react-router@*": dependency resolve to this older 4.0.23 when 4.0.27 exists (and I've added it manually?)

possibly related to #11917 but I don't really understand completely, so I could be wrong.

[ekilah]

by way of https://stackoverflow.com/a/49126573/2544629 I figured I'd give this a shot:

rm yarn.lock
yarn

which completely wipes out your yarn.lock and regenerates it. Maybe I could have done this another way, like removing and then re-adding all packages that required "@types/react-router@*" so that package was removed, but this worked out for me.

jjwatt99 , since it wasn't clear from your OP, you should try updating your types file for react-router by running yarn add @types/react-router . They've fixed the bug you're referring to there (DefinitelyTyped/DefinitelyTyped@5c516d0#diff-bc5f906a3af0cde1a95a8a23cb993e96).

[npenin]

Typescript is also complaining about indexed type:

type A={[key:string]:any}
function(a:keyof A)
{
    return a.substr(1);
}

In that case, should not it be enforced to be string only ?

[DanielRosenwasser]

Nicolas Penin (@npenin) a string index signature also implies the type can be indexed with a number given how JS coerces property names under the hood.

[typescript-bot]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.

[monstrege]

Extract<keyof T, string> did the trick for me.
I found this in Jordi Oliveras Rovira (@j-oliveras) 's post. Thx man!

[dominictobias]

I tried adding Extract but it did nothing, any ideas what I'm doing wrong?

function groupBy<T extends Record<K, PropertyKey>, K extends Extract<keyof T, string>>(
  items: readonly T[],
  key: K
) {
  return items.reduce((acc, item) => {
    (acc[item[key]] = acc[item[key]] || []).push(item);
    return acc;
  }, {} as Record<T[K], T[]>); // Still has an error at T[K]
}

Type 'T[K]' does not satisfy the constraint 'string'.ts(2344)
Type 'T[K]' does not satisfy the constraint 'string'.
  Type 'T[Extract<keyof T, string>]' is not assignable to type 'string'. // Huh?
    Type 'T[keyof T]' is not assignable to type 'string'.
      Type 'T[string]' is not assignable to type 'string'.
        Type 'string | number | symbol' is not assignable to type 'string'.
          Type 'number' is not assignable to type 'string'.ts(2344)

And if I do this:

function groupBy<T extends Record<K, PropertyKey>, K extends Extract<keyof T, string>>(
  items: readonly T[],
  key: K
) {
  return items.reduce((acc, item) => {
    (acc[item[key]] = acc[item[key]] || []).push(item);
    return acc;
  }, {} as Record<Extract<T[K], string>, T[]>);
}

The error goes away but I get new errors on the acc[item[key]] line: Type 'T[K]' cannot be used to index type 'Record<Extract<T[K], string>, T[]>'.ts(2536)

Edit The original code worked fine when I changed compileOptions.module from "ESNext" to "UMD" or "ES6" huh?