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27.2: Promises - Coggle Diagram

27.2: Promises

to avoid callbacks

fakeRequestPromise('yelp.com/api/coffee/page1')
    .then(() => {
        console.log("IT WORKED!!!!!! (page1)")
        return fakeRequestPromise('yelp.com/api/coffee/page2')
    })
    .then(() => {
        console.log("IT WORKED!!!!!! (page2)")
        return fakeRequestPromise('yelp.com/api/coffee/page3')
    })
    .then(() => {
        console.log("IT WORKED!!!!!! (page3)")
    })
    .catch(() => {
        console.log("OH NO, A REQUEST FAILED!!!")
    })

used to avoid

fakeRequestCallback('books.com/page1',
    function (response) {
        console.log("IT WORKED!!!!")
        console.log(response)
        fakeRequestCallback('books.com/page2',
            function (response) {
                console.log("IT WORKED AGAIN!!!!")
                console.log(response)
                fakeRequestCallback('books.com/page3',
                    function (response) {
                        console.log("IT WORKED AGAIN (3rd req)!!!!")
                        console.log(response)
                    },
                    function (err) {
                        console.log("ERROR (3rd req)!!!", err)
                    })
            },
            function (err) {
                console.log("ERROR (2nd req)!!!", err)
            })
    }, function (err) {
        console.log("ERROR!!!", err)
    })

let's write a version that uses Promises #

- - - - when the task is ongoing
    - - resolved
        
        if it concludes successfully
      - rejected
        
        if it fails
  - - - pass in a callback
        
        that will be called when
        
        the task resolves
    - - pass in a callback
        
        that will be called when
        
        the task rejects

fakeRequestPromise('yelp.com/api/coffee/page1')
    .then(() => {
        console.log("IT WORKED!!!!!! (page1)")
        fakeRequestPromise('yelp.com/api/coffee/page2')
            .then(() => {
                console.log("IT WORKED!!!!!! (page2)")
                fakeRequestPromise('yelp.com/api/coffee/page3')
                    .then(() => {
                        console.log("IT WORKED!!!!!! (page3)")
                    })
                    .catch(() => {
                        console.log("OH NO, ERROR!!! (page3)")
                    })
            })
            .catch(() => {
                console.log("OH NO, ERROR!!! (page2)")
            })
    })
    .catch(() => {
        console.log("OH NO, ERROR!!! (page1)")
    })

getting data

fakeRequestPromise('yelp.com/api/coffee/page1')
    .then((data) => {
        console.log("IT WORKED!!!!!! (page1)")
        console.log(data)
        return fakeRequestPromise('yelp.com/api/coffee/page2')
    })
    ...
    .catch((err) => {
        console.log("OH NO, A REQUEST FAILED!!!")
        console.log(err)
    })