Leverage the TypeScript Compiler API to verify whether an interface property signature permits the value of undefined (for example, prop1?:

Currently, I am utilizing the TypeScript Compiler API to extract Interface information in order to generate database tables. The process is functioning effectively, however, I am seeking a method to determine if certain fields are nullable, or as it is phrased in TypeScript terminology, have a type guard such as string|undefined.

For instance:

export default interface IAccount{
name: string;
description?: string;

}

I would like to be able to recognize the property "description" as string|undefined and thus, "nullable." While I can retrieve the node text using the compiler API and detect the presence of "?", I am curious if there is a more efficient approach available?

typescriptinterfacepropertiescompiler-constructionundefined

Answer №1

When looking at the InterfaceDeclaration node, we can find that it includes node.members which are essentially PropertySignature nodes. If a property signature within these members has a questionToken key, then it is considered nullable:

const str = `
interface IAccount {
  name: string;
  description?: string;
}
`;
const ast = ts.createSourceFile('repl.ts', str, ts.ScriptTarget.Latest, true /*setParentNodes*/);
const IAccount = ast.statements[0];
for (const member of IAccount.members) {
    const name = member.name.getText();
    let nullable = 'not nullable';
    if (member.questionToken !== undefined) {
        nullable = 'nullable';
    }
    console.log(`${name} is ${nullable}`);
}

The expected output would be:

name is not nullable
description is nullable

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