To remove undefined values from array with JavaScript, we call the filter method.

For instance, we write

const data = [42, 21, undefined, 50, 40, undefined, 9];

const newData = data.filter((element) => {
  return element !== undefined;
});

to call data.filter with a callback that checks if each element in data isn’t undefined.

Then items that aren’t undefined are returned in a new array.