Recursion on function-CodePudding

I developing a decorator to add middlewares to a AWS lambda, here is the source code. My inspiration in this, is the source code of mediator (Specifically, the class "RequestHandlerWrapperImpl" in this link). So I took the C# code and tried to pass it to Typescript. The simplified code is this.


// Used Types
type HandlerDelegate = () => Promise<APIGatewayProxyResult>;
type Handler = (event: APIGatewayProxyEvent) => Promise<APIGatewayProxyResult>
type Middleware = (event: APIGatewayProxyEvent, next: HandlerDelegate) => Promise<APIGatewayProxyResult>;

// Middlewares
const first = (event: APIGatewayProxyEvent, next: HandlerDelegate) =>{
  console.log("first in")
  const response = next();
  console.log("first out")

  return response;
};

const second = (event: APIGatewayProxyEvent, next: HandlerDelegate) =>{
  console.log("second in")
  const response = next();
  console.log("second out")

  return response;
};

// Executable logic
const read = forHandler(async () : Promise<APIGatewayProxyResult> 
      => APIResponse.createSuccess(HttpStatusCode.OK, "handler"))
  .addMiddleware(first)
  .addMiddleware(second)
  .finish;


// finish method

const finish = (event: APIGatewayProxyEvent) : Promise<APIGatewayProxyResult> => {
    let result: HandlerDelegate = () => handler(event);
        
    for (let i = 0; i < middlewares.length; i  ) {
        result = () => middlewares[i](event, result);

    }

    return result();
}

The expected log is this:

"first in"
"second in"
"handler"
"second in"
"first in"

But, is this, 'till a overflow exception

"second in"
"second in"
"second in"
"second in"
"second in"
"second in"
"second in"
"second in"

Can someone explain why ocurr this? I think is because at the line

result = () => middlewares[i](event, result);

I replace entirely the result variable (in both "sides"). So, instead of being recursive, it just loops. Also, how I can make it work as expected?

CodePudding user response：

The solution was modified the finish function, to this:

const finish = (event: APIGatewayProxyEvent) : Promise<APIGatewayProxyResult> => {
    let result: HandlerDelegate = () => {
        return handler(event);
    };
        
    for (let i = 0; i < middlewares.length; i  ) {
        let resultCallback = result; 
        result = () => {
            return middlewares[i](event, resultCallback);
        };
    }

    return result();
}

With this, the result function is not overwrited, and we make the pipeline work