Question

When combining assignment with comma (something that you shouldn’t do, probably), how does javascript determine which value is assigned? Consider these two snippets:

function nl(x) { document.write(x + '<br>'); } var i = 0; nl(i+=1, i+=1, i+=1, i+=1); nl(i); 

And:

function nl(x) { document.write(x + '<br>'); } var i = 0; nl((i+=1, i+=1, i+=1, i+=1)); nl(i); 

The first outputs

1 4 

while the second outputs

4 4 

What are the parentheses doing here?

Answer 1

I was confusing two things, here. The first call to ‘nl’ is a function call with four arguments. The second is the evaluation of the comma into one argument.

So, the answer: the value of a list of expressions separated by ‘,’ is the value of the last expression.