Question

55

JS async / await tasks queue

rated 0 times [ 62] [ 7] / answers: 1 / hits: 21596 / 6 Years ago, thu, november 29, 2018, 12:00:00

In my JS app I'm using the async / await feature. I would like to perform multiple API calls and would like them to be fired one after other. In other words I would like to replace this simple method:

const addTask = async (url, options) => {

    return await fetch(url, options)

}

with something more complex.. like:

let tasksQueue = []

const addTask = async (url, options) => {

    tasksQueue.push({url, options})

    ...// perform fetch in queue

    return await ...

}

What will be the best way to handle the asynchronous returns?

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tomas

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2 Years ago

answered 6 Years ago mckaylab · Accepted Answer

You could save previous pending promise, await for it before calling next fetch.

// fake fetch for demo purposes only

const fetch = (url, options) => new Promise(resolve => setTimeout(resolve, 1000, {url, options}))



// task executor

const addTask = (() => {

  let pending = Promise.resolve();

  

  const run = async (url, options) => {

    try {

      await pending;

    } finally {

      return fetch(url, options);

    }

  }



  // update pending promise so that next task could await for it

  return (url, options) => (pending = run(url, options))

})();



addTask('url1', {options: 1}).then(console.log)



addTask('url2', {options: 2}).then(console.log)



addTask('url3', {options: 3}).then(console.log)