Question

I have seen commas to concatenate primitive data types in Javascript and was wondering whether there was any difference in using a comma over say the + operator as well as the .concat() function?

So an example the following statement gives me abc

var value1 = a, value2 = b, value3 = c;
document.write(value1,value2,value3);

Answer 1

Since string concatenation is one of the haviest operations on computing, using document.write with various parameters would perform better.

See this test (it sometimes hangs in IE, so use other browser please) http://jsperf.com/document-write-vs-concatenation

Explaination:

document.write("val1", "val2", "val3");

is equivalent to

document.write("val1");
document.write("val2");
document.write("val3");

Thus, being much faster, since it doesn’t concatenates the strings.