JavaScript filter by two parameters

let results = dates.filter(e => {
  if(is_filter_by_arrival_date && is_filter_by_dept_date){
    return ( e.arrival_date <= arrival_to && e.arrival_date >= arrival_from &&
             e.departure_date <= dept_to && e.departure_date > = dept_from);
  }
  else if(is_filter_by_arrival_date){
    return e.arrival_date <= arrival_to && e.arrival_date >= arrival_from
  } else if(is_filter_by_dept_date) {
    return e.departure_date <= dept_to && e.departure_date > = dept_from
  }
  return true;
})

I think in your question you have just used arrival_to you should also make use of arrival_from. I have implemented according to my understanding.

Happy Coding!!

Just add the other filter as well? Also e.arrival_date <= arrival_to && e.arrival_date >= arrival_to is the same as e.arrival_date === arrival_to, since only that exact date can match. A date can never be both > and < than another date at the same time. So somthing like this might work:

const dates = [
  {arrival_date:'2019-01-01',departure_date:'2019-01-07'},
  {arrival_date:'2019-01-07',departure_date:'2019-01-09'},
  {arrival_date:'2019-01-10',departure_date:'2019-01-20'}
];

let is_filter_by_arrival_date = true;
let is_filter_by_dept_date = true;

let arrival_from = null;
let arrival_to = '2019-01-01';

let dept_from = null;
let dept_to = '2019-01-07';

let results = dates.filter( timeslot => {
  if ( is_filter_by_arrival_date && is_filter_by_dept_date ) {
    return timeslot.arrival_date === arrival_to && timeslot.departure_date === dept_to;
  }
  else if ( is_filter_by_arrival_date ) {
    return timeslot.arrival_date === arrival_to; 
  }
  else if ( is_filter_by_dept_date ) {
    return timeslot.departure_date === dept_to;
  }
  else throw new Error( 'no valid filters selected' );
});

console.log( results );

But I think you might have an error in your logic. If the idea is that the user can select a range of arrival and departure dates, hence else would you have both arrival_from and arrival_to, then you need to actually compare e.arrival_date <= arrival_to && e.arrival_date >= arrival_from instead of comparing to arrival_to both times. If this is true, then the code becomes:

const dates = [
  {arrival_date:'2019-01-01',departure_date:'2019-01-07'},
  {arrival_date:'2019-01-07',departure_date:'2019-01-09'},
  {arrival_date:'2019-01-10',departure_date:'2019-01-20'}
];

let is_filter_by_arrival_date = true;
let is_filter_by_dept_date = true;

let arrival_from = '2018-12-30';
let arrival_to = '2019-01-03';

let dept_from = '2019-01-07';
let dept_to = '2019-01-15';

let results = dates.filter( timeslot => {
  if ( is_filter_by_arrival_date && is_filter_by_dept_date ) {
    return timeslot.arrival_date >= arrival_from && timeslot.arrival_date <= arrival_to && timeslot.departure_date >= dept_from && timeslot.departure_date <= dept_to;
  }
  else if ( is_filter_by_arrival_date ) {
    return timeslot.arrival_date >= arrival_from && timeslot.arrival_date <= arrival_to
  }
  else if ( is_filter_by_dept_date ) {
    return timeslot.departure_date >= dept_from && timeslot.departure_date <= dept_to
  }
  else throw new Error( 'no valid filters selected' );
});

console.log( results );

The filter can be written shorter with ternaries and such as the other solutions show. But I preferred writing it out fully with if/else statements to make it more clear how the filter works.

You can use ternary operator like below for cleaner code

let results = dates.filter(e => {
  return (
    is_filter_by_arrival_date ? 
    // verify your condition for arrival date
    e.arrival_date <= arrival_to && e.arrival_date >= arrival_to 
    : 
    true
  ) && (
    is_filter_by_dept_date ? 
    // verify your condition for dept date
    : 
    true
  )
})

Just use some boolean algebra. bypass || condition will evaluate to true if bypass is set, otherwise whatever condition is:

 const result = dates.filter(({ arrivalDate, departureDate }) => {

    const arrivalFits = arrivalDate <= arrivalTo && arrivalDate >= arrivalTo;
    const departureFits = departureDate <= departureTo && departureDate >= departureTo;

   return (!filterByArrival || arrivalFits) && (!filterByDeparture || departureFits);
});