javascript

In this post, I will talk about running promises in parallel and optimizing for the lowest waiting time possible. When you have a bunch of promises that need to execute sequentially, you just run them in a sequence using .then() or awaits: getUser() .then(user => getPosts(user.id)) .then(posts => use(posts)); // Or let user = await getUser(); let posts = await getPosts(user.id); use(posts); But when they don’t depend on each other like the posts that need the user id, you can run them in parallel using Promise....

How we got here Promises marked a huge turning point in async js, they enabled a new type of control flow that saved us from callback hell. But some people found that calling .then() multiple times was too much, too callbacky. Then after a while, we resorted to generator functions and cogenerators, which made async code feel like its synchronous, at the cost of wrapping it in a generator function, yielding every line and introducing a cogenerator library (for example co) to deal with unwrapping the promises like the following example, where we could just yield a promise whenever we encounter it and pretend that the yield does not exist on that line of code....