I am trying to print the values inside the memo object, but I am getting undefined while is clear that there is values inside the memo object, or even iterating the object to get the values, please help.

let arr = [1, 2, 3, 4];

function iter(arr, n, memo = {}) {
  if (n < arr.length) {
    memo[n] = iter(arr, n   1);
  }

  // iterate memo object and print the values
  // memo = { '0': { '1': { '2': [Object] } } }
  for (let i in memo) {
    console.log(memo[i]);
    // I am getting undefined
  }
  // also here when I return the first value I am gettng undefined
  //
  return memo["0"];
}

console.log(iter(arr, 0));

CodePudding user response：

By doing

if(n < arr.length){
   memo[n] = iter(arr,n 1)
}

and

return memo['0']

at the bottom of the function, this means that:

• You don't pass memo along in the recursive call, so you're creating a new object each time iter runs. Even if you fix that -
• You return memo['0'] - but that 0 index is only assigned to at the very end of all the recursive calls. (n starts at 0, you enter recursion, then you eventually exit recursion, and finally at that point do you assign to memo[0] - not before - so before then, it's always undefined.)

If what you wanted was

memo = { '1': { '2': [Object] } }

then .reduceRight would be more appropriate to produce that structure. (memo isn't a good name because you aren't memoizing anything). The n variable doesn't look to be accomplishing anything here that .reduceRight can't handle by itself easier.

let arr = [1, 2, 3, 4];
function iter(arr, n) {
  return arr.reduceRight((prevValue, prop) => ({ [prop]: prevValue }));
}
console.log(iter(arr, 0))

If you wanted to use explicit recursion here, then perhaps something like

let arr = [1, 2, 3, 4];

function iter(arr, n) {
  return n === arr.length - 1
    ? arr[n]
    : { [arr[n]]: iter(arr, n   1) };
}

console.log(iter(arr, 0));

CodePudding user response：

let arr = [1,2,3,4];


function iter(arr,n,memo = {}){
    if(n < arr.length){
       memo[n] = iter(arr,n 1,memo)   iter(arr,n 1, memo)
    }


  for(let i in memo){
    console.log(i)
  }
  

}


console.log(iter(arr,0))