Why does javascript map function return undefined?

Question

My code

 var arr = [\'a\',\'b\',1];
 var results = arr.map(function(item){
                if(typeof item ===\'string\'){return item;}  
               });
<         


        

Answer 1

My solution would be to use filter after the map.

This should support every JS data type.

example:

const notUndefined = anyValue => typeof anyValue !== 'undefined'    
const noUndefinedList = someList
          .map(// mapping condition)
          .filter(notUndefined); // by doing this, 
                      //you can ensure what's returned is not undefined