JavaScript: better/cleaner functional way to find item from a nested array-CodePudding

I am trying to write a find function to find items from matched items from a potentially nested array (without having to flat the array first) and I am trying to write in a FP way.

Here is my attempt:

const nestedArray = [
  [{ id: 1 }],
  [{ id: 2 }],
  [{ id: 3 }, [{ id: 4 }]],
  { id: 5 },
]

function findTarget(arr, predicate) {
  const helper = ([x, ...xs]) =>
    x === undefined
      ? null
      : predicate(x)
      ? x
      : Array.isArray(x)
      ? helper(x) ?? helper(xs)
      : helper(xs)

  return helper(arr)
}

findTarget(nestedArray, (item) => item.id === 5)

I think it works but it is not super readable and I am sure there are better ways to write such a function.

CodePudding user response：

Here's how I would implement this using recursion:

function findTarget(value, predicate) {
  const isArray = Array.isArray(value);

  // Base case: if value is not array and predicate matches, we found a match
  if (!isArray) {
    if (predicate(value)) return value;
    return null;
  }

  // value must be an array, so run recursion and see if value exists
  for (const item of value) {
    const foundItem = findTarget(item, predicate);
    if (foundItem !== null) {
      return foundItem;
    }
  }

  // nothing found
  return null;
}

does the same thing that your code does and imo looks cleaner.

CodePudding user response：

Since your example is calling predicate(x) in the first place, it will return a false positive when matching an array with an id: 5 property, so the Array.isArray(x) should go first to avoid this:

const nestedArray = [
  Object.assign([{ id: 1 }], { id: 5 }),
  [{ id: 2 }],
  [{ id: 3 }, [{ id: 4 }]],
  { id: 5 },
]

function findTarget (arr, predicate) {
  if (!Array.isArray(arr))
    return predicate(arr) ? arr : null;
  let item, i = 0;
  for (; !item && i < arr.length;)
    item = findTarget(arr[i  ], predicate);
  return item ?? null;
}

const item = findTarget(nestedArray, (item) => item.id === 5);

console.log(item);