Question

While looking at a question related to porting a PHP function to JavaScript. I saw what I assumed was incorrect JavaScript:

function my_isnum(str, negative=false, decimal=false)

Then I tried this in JSFiddle:

function my_isnum(str, negative=false, decimal=-2)
{
    console.log(arguments);
    console.log(str);
    console.log(negative);
    console.log(decimal);
}
my_isnum("5", "Hi");

And to my utter amazement this is what I see in the Firebug console:

["5", "Hi"]
5
Hi
-2

Now in Chrome this is what I see:

Uncaught SyntaxError: Unexpected token = 

What I don’t understand is this an example of some early standard being supported by Firefox (the MDN on function doesn’t seem to mention this)?

Answer 1

This seems to be in the ECMAScript 6 specification and is at the moment only supported by Firefox

https://developer.mozilla.org/en-US/docs/JavaScript/Reference/default_parameters