How to return the entire array in a recursive JavaScript function?-CodePudding

I have a recursive function to work with nested arrays that are multi-level deep. The code below is supposed to select random elements, one from each level, and combine them into an array (in the order they are printed out in the console). However, the resulting array only contains elements of the highest levels (A, B or C, D or C), nothing below that. What is the reason for that?

const arry = [
  ["A"],
  ["B", "C"],
  ["D", "E"],
  [
    [
      ["F1", "F2"],
      ["G1", "G2"],
      [
        "H1",
        "H2",
        [
          ["I1", "I2", "I3"],
          ["J1", "J2"],
          ["K1", "K2", "K3"],
        ],
      ],
    ],
  ],
];

function rndmElementSelection(array) {
  rndElm = array[Math.floor(Math.random() * array.length)];
  return rndElm;
}

function recursion(array, resultAry = []) {
  array.forEach((element) => {
    if (typeof element === "string") {
      console.log(element);
      resultAry.push(element);
    } else {
      nE = rndmElementSelection(element);
      if (typeof nE === "string") {
        console.log(nE);
        resultAry.push(nE);
      } else {
        recursion(nE);
      }
    }
  });
  return resultAry;
}

console.log(recursion(arry));

CodePudding user response：

The problem is that your recursive call does not pass the second argument.

Without passing it, each recursive call will just populate its own, new array. It does return that array to the caller, but the caller (making the recursive call) ignores that returned value, so all the work of the recursive call is for nothing.

So the easy fix is to change this:

} else {
    recursion(nE);

to this:

} else {
    recursion(nE, resultAry);

CodePudding user response：

try this


function recursion(array, resultAry = []) {
  array.forEach((element) => {
    if (typeof element === "string") {
      console.log(element);
      resultAry.push(element);
    } else {
      nE = rndmElementSelection(element);
      if (typeof nE === "string") {
        console.log(nE);
        resultAry.push(nE);
      } else {
        resultAry = [...resultAry, ...recursion(nE)];
      }
    }
  });
  return resultAry;
}