JavaScript Promise Chaining: Mastering the Pipeline
Promise chains are more than then after then. Here is how I structure chains for transformation, branching, and error recovery. Promises chain by design: each then receives the resolved value of the previous promise and returns a new promise, letting you build pipelines that transform data step by step. Once I understood that a chain is a data pipeline and not just a sequence of callbacks, my async code became dramatically easier to reason about. Returning Values vs Promises Inside a then callback, you can return either a plain value or a promise. If you return a value, the next link in the chain receives it immediately. If you return a promise, the chain waits for it to resolve before continuing. This means you can mix synchronous transformation with asynchronous steps freely, and the chain handles the unwrapping automatically. fetch('/api/user/42') .then(res => res.json()) .then(user => user.profile.name) .then(name => name.toUpperCase()) .then(name => console.log(name)); Notice how each step narrows the data. The first then gives a Response, the next gives a user object, then a string, then an uppercased string. This progressive transformation reads top to bottom and is far clearer than…