AllowJS Not Working?

[sdrioux]

TypeScript Version: 3.1.1

Search Terms:
allowJS Implicitly has an 'any' type

TSConfig

{
    "compilerOptions": {
      "allowJs": true,
      "module": "commonjs",
      "noEmitOnError": true,
      "noFallthroughCasesInSwitch": true,
      "noImplicitReturns": true,
      "noUnusedLocals": true,
      "experimentalDecorators": true,
      "emitDecoratorMetadata": true,
      "moduleResolution": "node",
      "resolveJsonModule": true,
      "strict": true,
      "target": "es2017",
      "lib": [
        "dom",
        "es2017",
        "es2018",
        "esnext"
      ],
  }

I am importing this JS file:

module.exports = {
  development: {
    username: "postgres",
    password: "",
    database: "development_database",
    host: "127.0.0.1",
    dialect: "postgres"
  },
  test: {
    username: "postgres",
    password: "",
    database: "test_database",
    host: "127.0.0.1",
    dialect: "postgres",
    logging: false
  }
}

like this:

import { Sequelize } from 'sequelize-typescript'
import * as sequelizeConfig from '../db/config'

const config = sequelizeConfig[process.env.NODE_ENV || 'development']
...
...

Expected behavior:
On 3.0.3 this compiles fine with no issues.

Actual behavior:
On 3.1.1 I get this error:

Element implicitly has an 'any' type because type '{ development: { username: string; password: string; database: string; host: string; dialect: string; }; test: { username: string; password: string; database: string; host: string; dialect: string; logging: boolean; }; }' has no index signature.

7 const config = sequelizeConfig[process.env.NODE_ENV || 'development']

I'm new to Typescript, but shouldn't allowJS: true prevent this scenario?

When you set allowJs it means we check the JS file. That means we can infer a type for its output, which as you can see from the error message is { development: ..., test: ... }. When you index into that with [process.env.NODE_ENV || 'development'], there's an error because process.env.NODE_ENV could be anything, so we don't know that it's a valid key.
You could fix this with:

const env = process.env.NODE_ENV || 'development';
if (env !== "development" && env !== "test") throw new Error();
const config = sequelizeConfig[env]

(The reason this changed since 3.0 is because we no longer give an index signature to JS object literals in certain positions.)

[weswigham]

Yeah, as @Andy-MS said, we made it so noImplicitAny (a part of strict) opt you completely out of the implicit {[index: string]: any} index signatures objects originating in JS used to have (since it caused a ton of type safety issues, and the flag is supposed to help remove those).

[sdrioux]

Thank you! That worked.

Interestingly enough, this worked:

const env = process.env.NODE_ENV || 'development';
if (env !== "development" && env !== "test") throw new Error();
const config = sequelizeConfig[env];

This did not, and continued to throw the error:

const ENVIRONMENTS = ['development', 'test']

const env = process.env.NODE_ENV || 'development';
if (ENVIRONMENTS.includes(env) === false ) throw new Error();
const config = sequelizeConfig[env];

=== and !== are treated specially by TypeScript while includes is not.

[typescript-bot]

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