setting empty array in function argument

Question

I was going through JS practise code (for interview) and I saw that the instructor have used/assigned empty array in function parameter

function walk(collection, result = []) {
  collection.forEach(item => {
    if(isTheItem(item)) result.push(item);
    else walk(item[0].children, result);
  });
  return result;
}

In general, is the above code and the following code equal

  function walk(collection) {
      const result = []
      collection.forEach(item => {
        if(isTheItem(item)) result.push(item);
        else walk(item[0].children, result);
      });
      return result;
    }

Even from the recursive point of view? and if not, can someone please explain me the difference?

CertainPerformance · Accepted Answer · 2019-05-06 09:11:06Z

2

is the above code and the following code equal

No, because in your second code, walk only accepts one argument, and every call of walk (whether recursive or not) will have a new result. Your second code will currently only output items from the top level in the collection.

To fix the second code, you would have to accept a second argument to pass along the result, something like:

function walk(collection, result) {
  if (!result) {
    result = [];
  }
  collection.forEach(item => {
    if(isTheItem(item)) result.push(item);
    else walk(item[0].children, result);
  });
  return result;
}

answered May 6, 2019 at 9:11

CertainPerformance

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Comments

MikeB · Accepted Answer · 2019-05-06 09:11:53Z

2

That syntax is basically a placeholder - if no paramater is supplied as a function argument, then an empty array is assigned by default.

answered May 6, 2019 at 9:11

MikeB

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