How to dynamically create arguments as functions from an array

Question

I have an array of objects(can be of any length):

[
    {
        "operator": "sortBy",
        "value": "price"
    },
    {
        "operator": "startAt",
        "value": "7"
    },
    ...

]

where operator is a name of a function that can be imported from the JS module:

{
  sortBy: f(),
  startAt: f(),
  ...
}

and value is any value with a type of string or number.

How can I create functions from this array and pass them as arguments to another function?

For example:

import * as Utils from "@externalPackage";

const filters = [
    {
        "operator": "sortBy",
        "value": "price"
    },
    {
        "operator": "startAt",
        "value": "7"
    }
]

const anotherFunction = (arg1, arg2, ...) => ...
//this function can have any number of arguments

const helperFunction = (arr)=>//What should I do here with filters array to get a list of callable arguments(=>Utils.sortBy("price"), Utils.startAt(7)) ?//

const result = anotherFunction(helperFunction(filters)) 
                               ^ ^ ^
                               | | |
//This should be transformed in anotherFunction(Utils.sortBy("price"), Utils.startAt(7))//

You typed it out in pseudo code... Utils.sortBy("price"), you can simply translate that to a map call. const helperFunction = (arr)=> arr.map(({operator, value})=> (x) => Utils[operator](value)). But it's unclear how the Util functions are being called or what is being passed to them. Voting to close for clarity. — pilchard
– pilchard, Commented Aug 25, 2022 at 21:46
sortBy: f() should be sortBy: f. You don't want to call the function when creating the object, you just want to store a reference to the function in the object. — Barmar
– Barmar, Commented Aug 25, 2022 at 21:49
Assuming I'm reading correctly, you could build out the functions you need into strings then use something like this to parse them: gist.github.com/lamberta/3768814 — Porter Lyman
– Porter Lyman, Commented Aug 25, 2022 at 21:53

Lucjan Grzesik · Accepted Answer · 2022-08-25 21:58:42Z

2

You can use Array.map() to map the functions then you can spread it in arguments of another function. Then use the syntax as the one in the example to run the functions.

Utils['sortBy']('price')

const Utils = {
  sortBy: (a) => `sortBy ${a}`,
  startAt: (b) => `startAt ${b}`
}

const filters = [{
    "operator": "sortBy",
    "value": "price"
  },
  {
    "operator": "startAt",
    "value": "7"
  }
]

const anotherFunction = (arg1, arg2) => {
  console.log(arg1);
  console.log(arg2);
  
  return ':)';
}


const result = anotherFunction(...filters.map((f) => Utils[f.operator](f.value)))

edited Aug 25, 2022 at 21:58

answered Aug 25, 2022 at 21:47

Lucjan Grzesik

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1 Comment

Darryl Noakes Over a year ago

You need to spread the resulting array.

Darryl Noakes · Accepted Answer · 2022-08-25 21:52:41Z

1

Assuming you want the Util functions to be called immediately (e.g. they generate something, and that will be passed to the other function), you can use Array.map to map the filters into the results of calling the specified Util functions:

const mapFilters = (filters) => {
  return filters.map(({ operator, value }) => Utils[operator](value));
};

And then call the other function, spreading the resulting array as the parameters:

const result = anotherFunction(...mapFilters(filters));

edited Aug 25, 2022 at 21:52

answered Aug 25, 2022 at 21:46

Darryl Noakes

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