TypeScript Compiler API 函数，可以检查一个类是否实现了一个接口

Question

I wanted to check whether a ClassDeclaration of a file a.ts implements an InterfaceDeclaration from a file b.ts using Compiler API . But I couldn't find a method or a function for it.

function isClassImplementInterface(
  ts.ClassDeclaration: classDeclaration,
  ts.InterfaceDeclaration: interfaceDeclaration
): boolean {
  // return true if classDeclaration implements interfaceDeclaration correctly
}

Is there any function for it out of Compiler API?

Answer 1

To check if a class directly implements a certain interface you can look at the types of the implements heritage clause.

For example:

function doesClassDirectlyImplementInterface(
    classDec: ts.ClassDeclaration,
    interfaceDec: ts.InterfaceDeclaration,
    typeChecker: ts.TypeChecker
) {
    const implementsClause = classDec.heritageClauses
        ?.find(c => c.token === ts.SyntaxKind.ImplementsKeyword);

    for (const clauseTypeNode of implementsClause?.types ?? []) {
        const clauseType = typeChecker.getTypeAtLocation(clauseTypeNode);
        if (clauseType.getSymbol()?.declarations.some(d => d === interfaceDec))
            return true;
    }

    return false;
}

You may want to expand on that to also check if the class declaration has a base class and then check that class' heritage clauses as well.