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

You can implement like a below logic. Suppose you want an array of values.

let test = [ {name:'test',lastname:'kumar',age:30},
             {name:'test',lastname:'kumar',age:30},
             {name:'test3',lastname:'kumar',age:47},
             {name:'test',lastname:'kumar',age:28},
             {name:'test4',lastname:'kumar',age:30},
             {name:'test',lastname:'kumar',age:29}]

let result1 = test.map(element => 
              { 
                 if (element.age === 30) 
                 {
                    return element.lastname;
                 }
              }).filter(notUndefined => notUndefined !== undefined);

output : ['kumar','kumar','kumar']