Regex: are digit matches returned as string or number?

Question

Yesterday I was answering a question on stackoverflow, and there's something I don't understand in my own answer...

References: the thread in question, and my fiddle

Here is the code from my answer:

var rx = /{([0-9]+)}/g;
str=str.replace(rx,function(0,ドル1ドル){return params[parseInt(1ドル)];});

Now, what surprises me is that the following code works too:

var rx = /{([0-9]+)}/g;
str=str.replace(rx,function(0,ドル1ドル){return params[1ドル];});

My question: how come parseInt is not needed? At what point does JavaScript convert 1ドル into a number? Is it in the regex, or in the array?

• Wex: Have you tried using typeof?
• Christophe: doh...no, I should have started there. I just tried and it says string. So it seems that for the array 1 and '1' are the same.
• nhahtdh: I think of Array as Object, but with special treatment to keys that only contains non-negative numbers.

Answer 1

That is because javascript reads indexes as a string

array[1], will be converted to array['1'] before being read

The same way object['first'] will work

• Christophe: So using parseInt sounds rather stupid. I have updated my answer on the other post. Thanks... learning everyday.