_.isEmpty(obj, true)

var obj = {
  'firstName': undefined
, 'lastName' : undefined
};

console.log(_.isEmpty(obj)); // false
console.log(_.isEmpty({})); // true

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Please, see http://www.ericfeminella.com/blog/2012/08/18/determining-if-an-object-is-empty-with-underscore-lo-dash/

You can use _.isNil() to detect undefined or null. Since you're using Array.filter(), you want to return the results of !_.isNil(). Since i is supposed to be an object, you can use !_.isNil(i && i.id).

Note: you are using Array.filter() as Array.forEach(). The callback of Array.filter() should return a boolean, and the result of the filter is a new array.

const selectedItem = [
  undefined,
  {},
  { id: 5 },
  undefined,
  { id: 7 },
];

const result = selectedItem.filter(i => !_.isNil(i?.id));

console.log(result);

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You can also use _.reject() and save the need to add !:

const selectedItem = [
  undefined,
  {},
  { id: 5 },
  undefined,
  { id: 7 },
];

const result = _.reject(selectedItem, i => _.isNil(i?.id));

console.log(result);

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There's no isEmpty() method, you have to check for the type and the length:

if (typeof test === 'string' && test.length === 0){
  ...

The type check is needed in order to avoid runtime errors when test is undefined or null.