Create a Readable
stream that switches to the fallback on error
const {createReadStream} = require('fs');
const fallbackStream = require('fallback-stream');
fallbackStream([
createReadStream('foo.txt'), // foo.txt doesn't exist
createReadStream('bar.txt'), // bar.txt: 'Hello!'
createReadStream('baz.txt') // baz.txt doesn't exist
])
.pipe(process.stdout); // yields 'Hello!'
npm install fallback-stream
const fallbackStream = require('fallback-stream');
array: Array
(directly passed to multistream)
options: Object | Function | RegExp
Return: stream.Readable
When the first stream emits an error, the next one starts, and so on until one of the streams ends successfully. In other words, when the one of the streams ended, the rest won't be used.
const firstStream = fs.createReadStream('path/to/file/foo');
const fallback = fs.createReadStream('path/to/file/bar');
// a function that returns a readable stream
const fallbackFn = () => fs.createReadStream('path/to/file/baz');
fallbackStream([
firstStream,
fallback,
fallbackFn
]);
It supports stream.Readable
options and the following:
Type: Function | RegExp
Default: function() { return true }
Filter errors that streams emit. If the filtering result is falsy, the created stream emits an error immediately and won't use the rest of streams.
function createErrorStream(err) {
const stream = new stream.PassThrough();
process.nextTick(() => stream.emit('error', err));
return stream;
}
createStreams = function() {
return [
createErrorStream(new TypeError()),
createErrorStream(new RangeError()),
createErrorStream(new SyntaxError())
];
}
fallbackStream(createStreams(), {}).on('error', err => {
err.name; //=> 'SyntaxError'
});
fallbackStream(createStreams(), {
errorFilter(err) {
return err.name === 'RangeError';
}
}).on('error', err => {
err.name; //=> 'TypeError'
});
fallbackStream(createStreams(), {
errorFilter: /TypeError/
}).on('error', err => {
err.name; //=> 'RangeError'
});
You can directly pass a Function
or RegExp
to the second argument to specify the error filter simply, instead of passing an object.
fallbackStream([/* streams */], /ENOENT/);
Type: Error[]
Default: []
The Error
s that streams were supposed to emit but didn't.
Copyright (c) Shinnosuke Watanabe
Licensed under the MIT License.