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ndjson fetch API transformer
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const parseLine = (line) => { | |
try { | |
return JSON.parse(line); | |
} catch (e) { | |
} | |
}; | |
const ucasefirst = (str) => str.charAt(0).toUpperCase() + str.slice(1); | |
/* A simple wrapper that will turn a fetch response into a streaming emitter of JSON objects | |
* Usage: | |
* fetch(URI).then(response => ndjson(response) | |
* .on('data', data => { | |
* ... | |
* }) | |
* .on('error', err => { | |
* ... | |
* }) | |
* .on('end', () => { | |
* ... | |
* }) | |
* }) | |
*/ | |
const ndjson = (response) => { | |
const decoder = new TextDecoder(); | |
const reader = response.body.getReader(); | |
let buffer = ''; | |
const streamer = reader.read().then(function process(result) { | |
if (result.done) { | |
if (buffer.length > 0) { | |
const result = parseLine(buffer); | |
streamer.onData([result]); | |
} | |
streamer.onEnd(); | |
return; | |
} | |
buffer += decoder.decode(result.value, {stream: true}); | |
const lines = buffer.split("\n"); | |
buffer = lines.pop(); | |
const results = lines.filter(line => line.trim().length > 0).map(parseLine); | |
if (results.length > 0) { | |
streamer.onData(results); | |
} | |
return reader.read().then(process); | |
}).catch((e) => { | |
streamer.onError(e); | |
reader.cancel(); | |
streamer.onEnd(); | |
}); | |
streamer.onData = streamer.onError = streamer.onEnd = () => {}; | |
streamer.on = (event, handler) => { | |
streamer['on' + ucasefirst(event)] = handler; | |
return streamer; | |
}; | |
streamer.cancel = () => { | |
reader.cancel(); | |
streamer.onEnd(); | |
}; | |
return streamer; | |
}; | |
export default ndjson; |
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