Using operations to produce desired results in JavaScript

Problem

We are required to write a JavaScript function that takes in an array of exactly 4 numbers, arr, as the first argument and a target as the second argument.

Our function need to judge whether the numbers in the array arr could operated through *, /, +, -, (, ) to get the value equal to target.

For example, if the input to the function is

Input

const arr = [5, 3, 2, 1];
const target = 4;

Output

const output = true;

Output Explanation

Because we can achieve 4 like this −

(5 - 1) * (3 - 2) = 4

Example

Following is the code −

 Live Demo

const arr = [5, 3, 2, 1];
const target = 4;
const canOperate = (arr = [], target = 1) => {
   const isValid = x => Math.abs(x - target) < 0.0000001
   const helper = (arr = []) => {
      if (arr.length === 1) {
         return isValid(arr[0])
      }
      let valid = false
      for (let i = 0; i < arr.length; i++) {
         for (let j = i + 1; j < arr.length; j++) {
            const nextArr = arr.filter((x, index) => index !== i && index !== j)
            valid = valid || helper([...nextArr, arr[i] + arr[j]])
            || helper([...nextArr, arr[i] - arr[j]])
            || helper([...nextArr, arr[j] - arr[i]])
            || helper([...nextArr, arr[i] * arr[j]])
            || helper([...nextArr, arr[i] / arr[j]])
            || helper([...nextArr, arr[j] / arr[i]])
         }
      }
      return valid
   }
   return helper(arr)
}
console.log(canOperate(arr, target));

Output

true