How to write a function that returns an array of functions?

Question

Objective

Write a function values(f, low, high) that yields an array of function values [f(low), f(low + 1), . . ., f(high)].

What I Tried

function values(f, low, high) {
  var result = [];

  for(var i = low; i < high; i++) {
    result.push(j = f(i));
  }

  return result;
}

const vf = (p1) => console.log(p1);

const arrayOfFuns = values(vf, 10, 16);

console.log(arrayOfFuns);
console.log(arrayOfFuns[0]());

Expected Output

10
11
12
13
14
15
[ function, function, function, function, function, function ]
10 // console.log(arrayOfFuns[0]());

Output

10
11
12
13
14
15
[ undefined, undefined, undefined, undefined, undefined, undefined ]
/home/moss/var/Modern JS for the Impatient/3.3.js:16
console.log(arrayOfFuns[0]());
                          ^

TypeError: arrayOfFuns[0] is not a function
    at Object.<anonymous> (/home/moss/var/Modern JS for the Impatient/3.3.js:16:27)
    at Module._compile (internal/modules/cjs/loader.js:1072:14)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1101:10)
    at Module.load (internal/modules/cjs/loader.js:937:32)
    at Function.Module._load (internal/modules/cjs/loader.js:778:12)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:76:12)
    at internal/main/run_main_module.js:17:47

Why is the arrayOfFuns array element filled with undefined? I thought it would be an array of functions. Also I expected that accessing the first element of arrayOfFuns would print 10.

Shubham Pal · Accepted Answer · 2021-09-26 17:55:28Z

3

I think you are looking for something like this.

I have created a function named nf which returns the ith value and pushed it in the array.

function values(f, low, high) {
  var result = [];

  for(let i = low; i < high; i++) {
    f(i);
    const nf = () => i;
    result.push(nf);
  }

  return result;
}

const vf = (p1) => console.log(p1);

const arrayOfFuns = values(vf, 10, 16);

console.log(arrayOfFuns);
console.log(arrayOfFuns[0]());

answered Sep 26, 2021 at 17:55

Shubham Pal

807 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Unmitigated · Accepted Answer · 2021-09-26 17:47:24Z

2

You can create an anonymous function each time.

function values(f, low, high) {
  var result = [];

  for(var i = low; i < high; i++) {
    result.push(()=> f(i));
  }

  return result;
}

const vf = (p1) => console.log(p1);

const arrayOfFuns = values(vf, 10, 16);

console.log(arrayOfFuns);
console.log(arrayOfFuns[0]());

answered Sep 26, 2021 at 17:47

Unmitigated

91.4k12 gold badges102 silver badges109 bronze badges

Collectives™ on Stack Overflow

How to write a function that returns an array of functions?

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related