Search code examples
javascriptarrayspropertiessparse-matrix

What is "undefined x 1" in JavaScript?

I'm doing some small experiments based on this blog entry.

I am doing this research in Google Chrome's debugger and here comes the hard part.

What the heck is this?!

I get the fact that I can't delete local variables (since they are not object attributes). I get that I can 'read out' all of the parameters passed to a function from the array called 'arguments'. I even get it that I can't delete and array's element, only achieve to have array[0] have a value of undefined.

Can somebody explain to me what undefined x 1 means on the embedded image?

And when I overwrite the function foo to return the arguments[0], then I get the usual and 'normal' undefined.

This is only an experiment, but seems interresting, does anybody know what undefined x 1 refers to?

Solution

  • That seems to be Chrome's new way of displaying uninitialized indexes in arrays (and array-like objects):

    > Array(100)
[undefined × 100]

    Which is certainly better than printing [undefined, undefined, undefined,...] or however it was before.

    Although, if there is only one undefined value, they could drop the x 1.