JAVASCRIPT

js replace space with underscore

var string = "my name";
string = string.replace(/ /g,"_"); //returns my_name

javascript replace space by underscore

// replaces space with '_'
str = str.replace(/ /g, "_");
// or
str = str.split(' ').join('_');

replace space with underscore in c#

using System;
class Demo {
   static void Main() {
      String str, str2;
      str ="Hello World !";
      Console.WriteLine("String: "+str);
      str2 = str.Replace(" ", "-");
      Console.WriteLine("String (After replacing): "+str2);
   }
}