When comparing Parcel vs rollup, the Slant community recommends Parcel for most people. In the question“What are the best frontend JavaScript module bundlers?” Parcel is ranked 2nd while rollup is ranked 5th. The most important reason people chose Parcel is:
Run parcel watch on javascript file. It will auto download dependencies when you import modules.
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Pros
Pro Auto-fetch dependencies
Run parcel watch on javascript file. It will auto download dependencies when you import modules.
Pro Works nice with Vue.js
Just set "lang" parameter and parcel will install required dependencies like pug or node-sass. You don't even need to restart the process.
Pro Implements tree-shaking
Can reduce resulting bundle size by performing "tree-shaking" (removing unused parts of code).
Pro Easy configuration
Simple config files
Pro Small and fast installation
It's only one file.
Pro Ideal for shipping es2015/ES6 modules
Cons
Con Running yarn under the hood fails on Windows from time to time
Con Async/await support lack
Doesn't support async/await out of the box for the time being, and there is no available working plugin to fill the gap.