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streamUtils.js
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streamUtils.js
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const { Transform } = require('stream');
const map = (fn, options = {}) =>
new Transform({
// By default we are in object mode but this can be overwritten by the user
objectMode: true,
...options,
transform(chunk, encoding, callback) {
let res;
try {
res = fn(chunk);
} catch (e) {
return callback(e);
}
callback(null, res);
}
});
const filter = (fn, options = {}) =>
new Transform({
objectMode: true,
...options,
transform(chunk, encoding, callback) {
let take;
try {
take = fn(chunk);
} catch (e) {
return callback(e);
}
return callback(null, take ? chunk : undefined);
}
});
const reduce = (fn, acc, options = {}) =>
new Transform({
objectMode: true,
...options,
transform(chunk, encoding, callback) {
try {
acc = fn(acc, chunk);
} catch (e) {
return callback(e);
}
return callback();
},
flush(callback) {
callback(null, acc);
}
});
module.exports = { map, filter, reduce };