typescript convert to asynchronous

Question

I have the following functions:

function f (x : number): number {
 return 1/x
}

function g (x : number): number {
 return x*x
}

function h (x : number): number {
 return f(g(x))
}

I am trying to convert h (g and f too if needed) to an asynchronous function just with callbacks and not with promises but I am stuck with that.

I know that each function should have a function callback as a parameter but I am not sure how to do that.

These are inherently synchronous functions; what you you mean by converting them to async? — JohnnyHK
– JohnnyHK, Commented May 30, 2019 at 16:21

Paleo · Accepted Answer · 2019-05-30 16:15:37Z

3

We can start with f that provides an example of error management:

function f(x: number, cb: (err: any, result?: number) => void): void {
  if (x === 0)
    cb(new Error("Cannot call 'f' with zero"))
  else
    cb(null, 1/x)
}

Here is how to use it:

f(5, (err, result) => {
  if (!err)
    console.log("… do something with:", result)
})

The g function is easy:

function g(x: number, cb: (err: any, result?: number) => void): void {
    cb(null, x * x)
}

And h becomes to look like to a good old-fashioned callback hell:

function h(x: number, cb: (err: any, result?: number) => void): void {
    g(x, (err, gResult) => {
        if (err)
            cb(err)
        else
            f(gResult, cb)
    })
}

Thanks for this moment of nostalgia.

edited May 30, 2019 at 16:15

answered May 30, 2019 at 16:00

Paleo

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2 Comments

JohnnyHK Over a year ago

There's nothing async about this though. It's just really awkward synchronous code :)

Paleo Over a year ago

@JohnnyHK I assumed that the operations described in the question represented asynchronous stuff. We could write setTimeout but that's probably not what the author is looking for.

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