algorithm that calculates the result as the last number of the string

algorithm.js

let input = [1 , 1, 1, 1, 2];

let permutations = []
permutate([], {
  pos1: ['+', '-', '*', '/', '='],
  pos2: ['+', '-', '*', '/', '='],
  pos3: ['+', '-', '*', '/', '='],
  pos4: ['+', '-', '*', '/', '=']
})

  function permutate (currentVals, remainingAttrs) {
    remainingAttrs[Object.keys(remainingAttrs)[0]].forEach(attrVal => {
      let currentValsNew = currentVals.slice(0)
      currentValsNew.push(attrVal)

      if (Object.keys(remainingAttrs).length > 1) {
        let remainingAttrsNew = JSON.parse(JSON.stringify(remainingAttrs))
        delete remainingAttrsNew[Object.keys(remainingAttrs)[0]]

        permutate(currentValsNew, remainingAttrsNew)
      } else {
        permutations.push(currentValsNew)
      }
    })
  }

function check(input) {
  
  var parts = input.split('=');
  if (parts.length == 1) {
    return false;
  }

  var ans = true;
  var last = null;
  for (var i in parts) {
    var cur = eval(parts[i]);
    if (last == null) {
      last = cur;
    } else {
      ans = ans && (last === cur)
      last = cur
    }
  }

  return ans;
}

for (var i = 0; i < permutations.length; i ++) {
  var curPerm = permutations[i];
  var newInput = input[0] + curPerm[0] + input[1] + curPerm[1] + input[2] + curPerm[2] + input[3] + curPerm[3] + input[4] 
  if (check(newInput)) {
    console.log(newInput);
    break;
  }
}