on-error-resume-next

on-error-resume-next

Run a function, synchronously or asynchronously, and ignore errors.

The name come from Visual Basic. The original On Error Resume Next statement is considered a bad error handling practice.

Although the perception of the feature is negative, when scoped and used responsibly, it can become a very helpful utility function.

When using onErrorResumeNext, please be responsible and fully understand the impact of ignoring errors.

Breaking changes

New in 2.0

We introduced named exports and removed default imports. The default is synchronous. The "auto-detection" version is being moved to under 'on-error-resume-next/auto'.

- import onErrorResumeNext from 'on-error-resume-next';
+ import { onErrorResumeNext } from 'on-error-resume-next/auto';

It is recommended to use either synchronous or asynchronous version for better clarity.

Usage

onErrorResumeNext will return the result if it is a success. For example,

import { onErrorResumeNext } from 'on-error-resume-next';

// Will return result on returns.
const returned = onErrorResumeNext(() => JSON.parse('{"hello":"World!"}'));

expect(returned).toEqual({ hello: 'World!' });

// Will return undefined on throws.
const thrown = onErrorResumeNext(() => JSON.parse('<xml />'));

expect(thrown).toBeUndefined();

Notes: if an asynchronous function is being passed to onErrorResumeNext(), it will throw to protect from false negatives. Please use on-error-resume-next/async for asynchronous functions.

Asynchronous using async/await

onErrorResumeNext will capture both exceptions (synchronous) and rejections (asynchronous). The returned value is always a Promise object.

import { onErrorResumeNext } from 'on-error-resume-next/async';

// "async" will return Promise on resolves.
const resolution = onErrorResumeNext(() => Promise.resolve('Hello, World!'));

await expect(resolution).resolves.toBe('Hello, World!');

// "async" will return Promise on returns.
const returned = onErrorResumeNext(() => 'Hello, World!');

await expect(returned).resolves.toBe('Hello, World!');

// "async" will return Promise on rejects.
const rejection = onErrorResumeNext(() => Promise.reject(new Error()));

await expect(rejection).resolves.toBeUndefined();

// "async" will return Promise on throws.
const thrown = onErrorResumeNext(() => {
  throw new Error();
});

await expect(thrown).resolves.toBeUndefined();

Auto-detecting synchronous/asynchronous functions

For best experience, please use synchronous or asynchronous version instead.

on-error-resume-next/auto will handle both exceptions (synchronous) and rejections (asynchronous) accordingly.

import { onErrorResumeNext } from 'on-error-resume-next/auto';

// "auto" will return result on returns.
const returned = onErrorResumeNext(() => 'Hello, World!');

expect(returned).toEqual('Hello, World!');

// "auto" will return undefined on throws.
const thrown = onErrorResumeNext(() => {
  throw new Error('Hello, World!');
});

expect(thrown).toEqual(undefined);

// "auto" will return Promise on resolves.
const resolution = onErrorResumeNext(() => Promise.resolve('Hello, World!'));

await expect(resolution).resolves.toBe('Hello, World!');

// "auto" will return Promise on rejects.
const rejection = onErrorResumeNext(() => Promise.reject(new Error()));

await expect(rejection).resolves.toBeUndefined();

Sync vs. async vs. auto

The following table show how each version react with different passing functions.

	Default (sync)	Async	Auto
return 1	1	Promise.resolve(1)	1
throw 2	undefined	Promise.resolve(undefined)	undefined
Promise.resolve(3)	Not supported, will throw	Promise.resolve(3)	Promise.resolve(3)
Promise.reject(4)	Not supported, will throw	Promise.resolve(undefined)	Promise.resolve(undefined)

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