Convert array into upper case

you should use handler function in map:

var array2 = ["melon","banana","apple","orange","lemon"];
array2 = array2.map(function(x){ return x.toUpperCase(); })

for more information about map

edit: yes you can do

toUpper = function(x){ 
  return x.toUpperCase();
};
array2 = array2.map(toUpper);

you can use this :

var a = ['this','is','test'];

a.map(f=>{ return f.toUpperCase(); });

toUpperCase() do not change the value. Try

array2 = array2.map(function (e) { 
    return e.toUpperCase()
});