incepto

Incepto - Inline Try - Catch Clause for Async Functions

Installation

npm i incepto -s

Usage

const incepto = require("incepto");

// Latin Usage
async function myFunc() {
  const result = await incepto(throwableAsyncFunction()).capturam(
    "Function Failed"
  );
  return result;
}
// English Usage
async function myFunc() {
  const result = await incepto(throwableAsyncFunction()).catch(
    "Function Failed"
  );
  return result;
}
// If function throws, below line will throw an Error object with the "Function Failed" argument in construction
const result = await myFunc();

/**
 * We can override the error handler and provide alternative behaviour.
 * The error handler takes two arguments as input, the actual error in
 * the first element and the custom message or object passed to "catch"
 * in the second element.
 */
// Latin Usage
incepto.tracto = (e, message) => message;
// English Usage
incepto.errorHandler = (e, message) => message;

/**
 * For instance, asynchronous servers can benefit from this package
 * such as fastify by creating a custom error handler and creating
 * a custom Error object in the error handler.
 */
// Custom Error Class
class HTTPException extends Error {
  constructor(code, message) {
    super(message);
    this.status = code;
    this.error = message;
  }
}
// Declare Verbose Error Code Packs
const NOT_FOUND = [404, "Not Found"];
// Set the Error Handler to throw an HTTPException and deconstruct the Error Code Pack
incepto.errorHandler = (e, ERROR) => throw new HTTPException(...ERROR);
// Override default error handler by extracting the status and error of the HTTPException and if it does not exist, assign default values
fastify.setErrorHandler(
  ({ status = 500, error = "Internal Server Error" }, req, reply) => {
    reply.status(status).send({ error });
  }
);
// Use incepto with asynchronous functions that might throw
fastify.get("/", async (req, res) => {
  const result = await incepto(throwableAsyncFunction()).catch(NOT_FOUND);
});
/**
 * Another use case for the library, apart from cleaner code,
 * is its usage within libraries to return an err variable
 * wherever the code throws.
 */
incepto.errorHandler = (e, ERROR) => {
  return { err: { message: ERROR, info: e } };
};
async function myAPI() {
  const result = await incepto(throwableAsyncFunction()).catch("Failed");
  return { data: result.data };
}
const { err, data } = await myAPI();
if (err !== undefined) {
  console.log(err.message);
  console.error(err.info);
}
// Continue Execution

Description

This plugin introduces an inline try-catch approach. While the name try would be more preferable, it is a reserved keyword and attempt was taken on npm so I chose to name it incepto after the latin translation of "attempt".

It takes a Promise as input (async functions by default return a Promise when invoked) and, after calling catch, capture or capturam ("catch" in latin) with what you wish to pass to the error handler or throw via the default behavior, it attempts to resolve the Promise and on failure executes its error handler.

The default behaviour is to throw with what was passed in catch etc. as in the following line:

throw new Error(catchInput);

Options

You can override the default throw behaviour by overriding the errorHandler or tracto ("handler" in, you guessed it, latin) variable of the function object. With it, you can choose to return a value, throw a specific type of error or whichever you basically wish.

Author

Alex Papageorgiou

License

Licensed under GPLv3.