; | |
const pLimit = require('p-limit'); | |
class EndError extends Error { | |
constructor(value) { | |
super(); | |
this.value = value; | |
} | |
} | |
// The input can also be a promise, so we await it | |
const testElement = async (element, tester) => tester(await element); | |
// The input can also be a promise, so we `Promise.all()` them both | |
const finder = async element => { | |
const values = await Promise.all(element); | |
if (values[1] === true) { | |
throw new EndError(values[0]); | |
} | |
return false; | |
}; | |
const pLocate = async (iterable, tester, options) => { | |
options = { | |
concurrency: Infinity, | |
preserveOrder: true, | |
...options | |
}; | |
const limit = pLimit(options.concurrency); | |
// Start all the promises concurrently with optional limit | |
const items = [...iterable].map(element => [element, limit(testElement, element, tester)]); | |
// Check the promises either serially or concurrently | |
const checkLimit = pLimit(options.preserveOrder ? 1 : Infinity); | |
try { | |
await Promise.all(items.map(element => checkLimit(finder, element))); | |
} catch (error) { | |
if (error instanceof EndError) { | |
return error.value; | |
} | |
throw error; | |
} | |
}; | |
module.exports = pLocate; | |