functional-try

Error handling wrapper for cleaner use of strict type checking in TypeScript

This library is intended to replace await-to-js in projects using TypeScript with strict settings.

Install

npm i functional-try

Usage

Import

import { trySync, tryAsync } from 'functional-try';

Synchronous

trySync takes a function and the parameters to invoke it with. It will synchronously call the function, automatically catch any errors, and return an object containing the function's result or caught error.

const parsedJson = trySync(JSON.parse, fileString);

if (parsedJson.failure) {
    console.log('Error parsing JSON', parsedJson.error);
    return;
}

// TypeScript recognises `value` must have a value here
// since the failure state is handled
handleSuccess(parsedJson.value);

Asynchronous

tryAsync takes a promise and returns another promise that resolves to an object containing the first's result or caught error.

const asyncRes = await tryAsync(someAsyncFunction(params));

if (asyncRes.failure) {
    console.log('Error calling async function', asyncRes.error);
    return;
}

// TypeScript recognises `value` must have a value here
// since the failure state is handled
handleSuccess(apiRes.value);

Motivation

I use await-to-js quite extensively in TypeScript projects, with a pattern similar to:

const [err, res] = await to(someAsyncFunction(params));

if (err) {
    handleError(err);
    return;
}

doSomethingWithRes(res);

But this doesn't work well with strict typing. Even though the return type of to indicates that err and res should be mutually exclusive, TypeScript still thinks res is possibly undefined due to the deconstruction severing the logical connection between the two.

This can be avoided by just not deconstucting:

const asyncRes = await to(someAsyncFunction(params));

if (asyncRes[0]) {
    handleError(asyncRes[0]);
    return;
}

handleSuccess(asyncRes[1]);

In this case TypeScript knows that by the time handleSuccess is called asyncRes[1] has a value because asyncRes[0] doesn't, avoiding the type error. But this doesn't result in very readable code.

This package functions nearly identical to await-to-js, just returning an object instead of a tuple, making usage without deconstruction cleaner.