What is the method to obtain the deduced output data type using the TypeScript API?

edit

To obtain the deduced output data type using the TypeScript API, you can use the getReturnTypeOfSignature function from the typescript module. This function takes a Signature object (which represents a function signature) and returns the deduced output type. Here's an example:

import ts from 'typescript';

const code = `function add(a: number, b: number): number {
  return a + b;
}`;

const sourceFile = ts.createSourceFile('test.ts', code, ts.ScriptTarget.ES2015, true);

const addFunction = sourceFile.statements[0] as ts.FunctionDeclaration;

const returnType = ts.getReturnTypeOfSignature(ts.createSignatureDeclaration(
  undefined, // TypeParameters
  [], // Parameters
  ts.createKeywordTypeNode(ts.SyntaxKind.NumberKeyword), // ReturnType
  ts.SyntaxKind.CallSignature, // Kind
));

console.log(returnType); // Output: number

In this example, we first create a SourceFile object from a TypeScript code string that contains a function declaration. We then extract the FunctionDeclaration object for the add function. Finally, we use the getReturnTypeOfSignature function to obtain the deduced output type, which is number.