Mistakes we make using JavaScript Promises

Post by borschtplease » Fri, Jul 05, 2019, 1:07 AM UTC

Post by TheCycoONE » Fri, Jul 05, 2019, 1:33 AM UTC

jchw wrote: post #3

borschtplease wrote: post #2

And he makes mistake #1 in mistake #3 by running „get“ sequentially instead of using Promise.all

They're all artificial examples: one could assume that the tasks in #3 are intended to be executed serially. Though there aren't any data dependencies expressed between the different calls, perhaps ordering could be important for other reasons.

Post by franciscop » Fri, Jul 05, 2019, 1:55 AM UTC

    get("http://data.com/user") 
      .then(user => get("http://data.com/location" + user.id))
      .then(location => createEntry(user, location)) 
      .then(response => {
        // handle response 
      }).catch(err => {
        // handle failure
      });

    get("http://data.com/user") 
      .then(user => get("http://data.com/location" + user.id)
        .then(location => createEntry(user, location)))
      .then(response => {
        // handle response 
      }).catch(err => {
        // handle failure
      });

    try {
      const user = await get("http://data.com/user"); 
      const location = await get("http://data.com/location" + user.id);
      const response = await createEntry(user, location);
      // handle response 
    } catch (error) {
      // handle failure
    }

Post by betamark » Fri, Jul 05, 2019, 1:59 AM UTC

Post by jchw » Fri, Jul 05, 2019, 2:29 AM UTC

TheCycoONE wrote: post #4

jchw wrote: post #3

Earlier quoted context omitted.

They're all artificial examples: one could assume that the tasks in #3 are intended to be executed serially. Though there aren't any data dependencies expressed between the different calls, perhaps ordering could be important for other reasons.

I feel it should have been called out explicitly when introducing await, because the 'clean' solution in async/await code is to call each async function and then await the results where you need them - which is a pattern he doesn't hint at at all.