How do you convert a callback-based function to a promise in JavaScript?
Wrap it in a new Promise. Call the original function with a callback that calls reject on error and resolve on success. Return the promise. The callback must follow the error-first convention: (err, result) => {}.
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More FAQs in Converting Callbacks to Promises in JavaScript
A built-in utility that converts a callback-based function (error-first convention) to a promise-based one. Usage: const readFileP = promisify(fs.readFile). Then use it with .then or async/await.
Yes. Many APIs have promise-based versions. Use require('fs').promises or require('fs/promises') for file system, for example. No need to promisify manually. Use them with async/await.
Use new Promise with emitter.once: new Promise((resolve, reject) => { emitter.once(event, resolve); emitter.once('error', reject); }). Node.js provides events.once(emitter, event) for this.
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