With-fallback NPM

with-fallback

Wraps a function with a fallback value which will be returned in case the function fails.

setup

npm install with-fallback

usage

import withFallback from 'with-fallback'

async function fetchUserImage(uid) {
    const userResponse = await fetch(`https://my-server/api/users/${uid}`);
    const userDto = await userResponse.json();
    return userDto.image;
}

const defaultImage = {
    url: 'default_profile.png',
    width: 50,
    height: 50,
};

const userImage = withFallback(() => fetchUserImage(1), defaultImage);

Api

`withFallback(`fetcher, fallback, options`)`:

Arguments:

fetcher: () => Promise<ValueType> - an async / sync function that returns a value of type \.
fallback: ValueType - a fallback value of type \ that will be returned in case fetcher fails (throws)
options: WithFallbackOptions:
- logger: (error: Any) => void - a logger which will be invoked when a fallback occours. (default logger is console.log)
- retry: RetryOptions:
  - amount: number - the maximum amount of retries to perform (default amount is 0)
  - duration: number - waiting time between retries - in ms (default duration is 1000 ms)
- verifier: (response: ValueType) => boolean - a function that verifies the response if it didn't throw an error
- backupFetcher: () => Promise<ValueType> - a secondary fetcher that will be tried if the main fetcher fails (it will invoke alternatively when using retry and be verified and logged)

Return Value:

Promise<ValueType>

`fetchResponseVerifier`:

Provide as a verifier to handle fetchApi requests

import withFallback, { fetchResponseVerifier } from 'with-fallback'

const userImage = withFallback(() => fetch(`https://my-server/api/users/${uid}`), fallback, { 
        verifier: fetchResponseVerfier
});

This verifies that the response is "ok"