CODEWITHSUNDEEP
typescriptabstract-syntax-treetypescript-compiler-api
Daniel Wolf
Daniel Wolf

Reputation: 13663

How to analyze Type object from TypeScript compiler API?

Note: This question is about the TypeScript compiler API, not about TypeScript as a language!

I have a value of type ts.Type. I want to know what type it represents: Is it a number? A function? An array?

I found that type.flags allows me to perform roughly the static equivalent of the typeof operator, allowing me to differentiate between primitive types such as number, string, and boolean (but not functions). Anything else -- arrays, functions, POJOs, etc. -- simply has the TypeFlags.Object flag.

How can I further examine these non-primitive types? How do I determine whether a type is an array, a function, an enum, a class instance...?

Upvotes: 3

Views: 348

Answers (2)

drewish
drewish

Reputation: 9380

First off I'd say go play around with https://typescript-eslint.io/play/. Drop in some code, select the TypeScript tab, and click around. As you select notes in the tree it'll show you decoded values of the kind and flags properties.

It's much nicer than the helper I'd started off with to decode the flags:

function activeFlags(flagEnum: any, flagValue: number) {
    return Object.entries(flagEnum)
        .filter(([, value]) => typeof value === 'number' && (flagValue & value) !== 0)
        .map(([key]) => key);
}

activeFlags(ts.NodeFlags, tsNode.flags);

Upvotes: 0

Renzhentaxi Baerde
Renzhentaxi Baerde

Reputation: 556

There is another field on types that have Typeflags.Object. Its called type.objectFlags and you can use it to further distinguish the type

Upvotes: 0

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