Concatenating many/long strings can significantly slow down the performance of your application, especially in Internet Explorer (see this website).

Using string buffers is always good practice when working with large lists of strings. For small lists of strings, it is more efficient to simply concatanate strings.

Even though JavaScript doesn't have this functionality, you can emulate it.

Bad behavior:

var string = "";
for (var i = 0; i < 10000; i++) { 
  string += "foo"; 
}

Good behavior:

var stringList = [];
for (var i = 0; i < 10000; i++) { 
  stringList.push("foo"); 
}
var string = stringList.join("");