javascript - filtering only if it is not null or undefined

Question

     results.data
              .filter((x) => countries.includes(x.country))
              .filter((x) => x.car_model_year > startYear && x.car_model_year < endYear)
              .filter((x) => x.gender.toLowerCase() === gender.toLowerCase())
              .filter((x) => colours.includes(x.car_color)),

I have this piece of code above countries, startYear, endYear, gender and colours are variables that can be null or undefined. The issue is it should ignore the filteration for that specific variable if the variable is empty(null or undefined). What is the best way to implement it, thank you.

Answer 1

You can check if a value is null or undefined by comparing it to null (see this answer), so just OR that check into each of your filter expressions and they will only filter if the value is not null or undefined.

results.data
       .filter((x) => countries == null || countries.includes(x.country))
       .filter((x) => startYear == null || endYear == null || x.car_model_year > startYear && x.car_model_year < endYear)
       .filter((x) => gender == null || x.gender.toLowerCase() === gender.toLowerCase())
       .filter((x) => colours == null || colours.includes(x.car_color))