How to avoid undefined in string concatenation?

Question

I\'m iterating over an object and I want to concatenate the name of the service. This is my code:

var servizi;

for(var i = 0; i < appointment.id_services         


        

Answer 1

You get undefined because you declared an uninitialized variable, and then added to it (twice).

Initialize the declared variable as an empty string first

var servizi = "";

Answer 2

intialize variable to empty string

var servizi = "";