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LFW211 lab 8.1

abdullah.yf
abdullah.yf Posts: 2
in LFW211 Class Forum

I think I solved the 8.1 lab correctly but I need someone expert in the matter to check the work as the solution felt a bit weird!

const print = (err, contents) => { 
  if (err) console.error(err)
  else console.log(contents )
}

const opA = (err,cb) => {
  setTimeout(() => {
    cb(null, 'A')
  }, 500)
}

const opB = (err,cb) => {
  setTimeout(() => {
    cb(null, 'B')
  }, 250)
}

const opC = (err,cb) => {
  setTimeout(() => {
    cb(null, 'C')
  }, 125)
}

opA(null,print)
opB(null,print)
opC(null,print)

Best Answer

  • davidmarkclements
    davidmarkclements Posts: 270
    Answer ✓

    @abdullah.yf yep this completes the exercise, nice job

    @SyuheiSaito these functions don't return anything, so shouldn't be passed to then, they also have signatures that expect err and cb functions, where as then passes the prior promise into the function. Finally, chaining promises like that means the code will execute serially, and what we want is for it to execute concurrently.

Answers

  • k0dard
    k0dard Posts: 93

    Hello,
    I'm not the expert but since the lab name is parallel execution I guess your solution is OK

  • abdullah.yf
    abdullah.yf Posts: 2

    thank you

  • SyuheiSaito
    SyuheiSaito Posts: 7

    I've failed 8-1

    `const print = (err, contents) => {
    if (err) console.error(err)
    else console.log(contents)
    }

    const opA = (err,cb) => {
    setTimeout(() => {
    cb(null, 'A')
    }, 500)
    }

    const opB = (err,cb) => {
    setTimeout(() => {
    cb(null, 'B')
    }, 250)
    }

    const opC = (err,cb) => {
    setTimeout(() => {
    cb(null, 'C')
    }, 125)
    }

    let promise = new Promise(print)

    promise.then(opA(null,print))
    .then(opB(null,print))
    .then(opC(null,print))`

  • dtravailloux
    dtravailloux Posts: 16

    Imho we don't need to change the lab code like @abdullah.yf, just do that no ?

    opA(print);
    opB(print);
    opC(print);

  • davidmarkclements
    davidmarkclements Posts: 270

    @dtravailloux that doesn't match the function signatures. The functions take take two arguments (err, cb).

    The main point of this exercise is to demonstrate the non-linear execution of code in the concurrency-based JS language

  • theodoros
    theodoros Posts: 17

    Hi @davidmarkclements, i m a bit confused.
    I too see what @dtravailloux sees, as function signature, on parallel.js and on the lab description.

    The functions opA, opB & opC, they take just ONE parameter and this is the cb, like so:

    const opA = (cb) => {
    setTimeout(() => {
    cb(null, 'A')
    }, 500)
    }

    Based on the above, the correct solution should be:

    opA(print)
    opB(print)
    opC(print)

  • krave
    krave Posts: 45

    Hi @theodoros , the corect solution for labs 8.1 is the same as yours in my opinion.
    All the tasks could just start in parallel.

    For labs 8.2, opA, opB and opC are just simulations to callback-based async functions.
    These functions will do their own async jobs. In most cases we don't what exactly they do.
    But we know that if there will not be errors, they finished their jobs successfully.

    After their sucess, they will invoke the callback - cb you passed to them. And the arguments passed to the callback you provide, will be error first, then the results based on their works(those async tasks).

    So the signatures of opA, opB and opC take just ONE parameter is correct!
    What matters is the signatures of cbs you provide.

    But if you promisify opA, opB and opC, promisify will take care of the cbs for you. You don't really need think about them.

  • davidmarkclements
    davidmarkclements Posts: 270

    good answer @krave

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