safe-assignment

Error Safe Assignment alternative for JS/TS, a simple way to remove try/catch hell

Why

The ECMAScript Safe Assignment Operator Proposal is to add a new operator to JavaScript that would allow for safe assignment of values, removing the need for try-catch blocks in many cases.

Since it is in a very early stage and not yet implemented in any JavaScript engine, this package provides a simple utility function that wraps a function or promise in a try-catch block, returning a tuple containing an error or undefined and the result of the function or promise.

Status

The library is an experimental utility to provide a simple way to remove try-catch hell, and in a very early stage, so the API may change in the future.

Currently it should be safe for production use, but we recommend using it with caution, and postpone using it in critical projects or business project until it is more stable.

Hobby projects, side projects, and small projects are good candidates for using this library.

Installation

You can install the package using npm:

npm install safe-assignment

Usage

The safeTry function is a utility that wraps a function or promise or any value in a try-catch block, returning a tuple containing an error or undefined and the result of the function or promise.

API

safeTry

A utility function that wraps a function or promise in a try-catch block.

Parameters

input (Function | Promise<unknown> | unknown): The function or promise to be wrapped.

Returns

A tuple containing an error or undefined and the result of the function or promise.

One of the error or data would be undefined, and the other would be the result or error, so undefined detection is necessary to narrow the type, or use optional chaining operator ?. to avoid runtime error.

• When the input is a function, return a wrapped function, which accept the same parameters as the original function, and will return the tuple.
  • if the input function is asynchronous, the wrapped function will return a promise as well.
• When the input is a promise, the promise is awaited and the result is returned.
• When the input is neither a function nor a promise, the input is returned, the error always undefined.
  • so its possible to pass undefinedornullas input, for example, the optional chaining operator?.`

Limitations

• if the input function should not implicit returns any, it messed up the type inference, so it`s better to define the return type explicitly.

import { safeTry } from 'safe-assignment';

// Synchronous function
safeTry(() => 42)(); // Output: [undefined, 42]

// Synchronous function with error
safeTry(() => {
    throw new Error('sync error');
})(); // Output: [Error('sync error'), undefined]

// define error type generic
safeTry<Error>(Promise.reject(new Error('xxx'))) // Output: [Error('xxx), undefined]

// Asynchronous function
await safeTry(async () => 42)(); // Output: [undefined, 42]

// Asynchronous function with error
await safeTry(async () => {
    throw new Error('async error');
})(); // Output: [Error('async error'), undefined]

// Promise
const [promiseError, promiseResult] = await safeTry(Promise.resolve(42)); // Output: [undefined, 42]

// Promise with error
const [promiseError2, promiseResult2] = await safeTry(Promise.reject(new Error('promise error'))); // Output: [Error('promise error'), undefined]

// input optional
const [,optionalResult] = await safeTry(preResult?.run()); // Output: [Error?, undefined | Result]

Examples

Before:

let data: SomeType;

try {
    data = serializeQuery();
} catch (error) {
    // promise.reject or throw works well, but if want to do some thing fallback, you should catch errors
    console.error(error);
}

// anyway there should detect data, or return in cache, or use data! to avoid undefined
if (!data) {
    return;
}

let result;
try {
    result = await fetch(data);
} catch (error) {
    console.error(error);
}

return result;

After:

import { safeTry } from 'safe-assignment';

const [serializeError, data] = safeTry(serializeQuery)();
if (serializeError) {
    console.error(serializeError);
    return;
}

const [fetchError, result] = await safeTry(fetch(data));
if (fetchError) {
    console.error(fetchError);
    return;
}

return result;

// or if want to ignore error
const [, result2] = await safeTry(fetch(data));
result2 && console.log(result2); // undefined detection of error or result is necessary to narrow type