How to get features in typescript without casting?

[nkint]

Question:

Hi!
Thank you for the great library! I was looking for a typescript audio feature analysis for a while and.. 🚀⚡️💥

Sorry this is my first question and it might be dumb and born out of lack of examples.

I'm in typescript, and I'd like to understand how to retrive one single feature without casting.

type State = {
  energy: null | number
}

const state: State = {
  energy: null
}

// ... down into retrieve audio features
state.energy = meydaAnalyzer.get('energy') // ERROR HERE

I get the error:

Type 'Partial<MeydaFeaturesObject>' is not assignable to type 'number'.

I'm solving it with brutal casting:

state.energy = meydaAnalyzer.get('energy') as number

I don't have any specific settings and this error seems to be quite general and linked to a too miuch flexible .get typings, but I'm sure you have a better solution.

Enviroment:

For completeness this is my setup (I don't think it is important but, you know...):

versions:

"meyda": "^5.4.0",
"typescript": "^4.6.4",
"vite": "^2.9.9",

and my tsconfig.json:

{
  "compilerOptions": {
    "target": "ESNext",
    "lib": ["DOM", "DOM.Iterable", "ESNext"],
    "types": ["vite/client"],
    "baseUrl": "src",
    "allowJs": true,
    "skipLibCheck": false,
    "esModuleInterop": true,
    "allowSyntheticDefaultImports": true,
    "strict": true,
    "forceConsistentCasingInFileNames": true,
    "module": "ESNext",
    "moduleResolution": "node",
    "resolveJsonModule": true,
    "isolatedModules": true,
    "noEmit": true,
    "jsx": "react",
    "downlevelIteration": true,
    "alwaysStrict": true,
    "strictNullChecks": true
  },
  "include": ["./src"],
  "exclude": ["node_modules"]
}

[hughrawlinson]

Hi!

I've actually been working on a PR for this - it's not ready at the moment and the complexity make me think maybe it's not the right thing to merge for maintainability reasons. I would love feedback on the design described here though!

For now, I would suggest writing a user defined type guard function.

[nkint]

Hi @hughrawlinson thanks for the answer!

I was thinking to replace .get to my own typed get function:

type FeatureName = keyof MeydaFeaturesObject
function getFeatures <KS extends FeatureName>(keys: readonly KS[]): Pick<Features, KS> {
   return meydaAnalyzer.get(keys)
}

the new extract API seems very interesting! 👏