Array.prototype.slice web-compat issue?

Boris Zbarsky bzbarsky at MIT.EDU
Tue Sep 10 18:04:43 PDT 2013

On 9/10/13 7:32 PM, Allen Wirfs-Brock wrote:
> What do you think people are actually testing for when they do Array.isArray?

It varies, but some things I've seen people test for via "is array" methods:

1)  Polymorphic methods that take an "array" or "something else".  Just 
looking at a random sampling of JS right now, I see a function that 
takes as its first argument a URI or array of URIs, a function that 
takes a colorspace or array of colorspaces, a function that takes a 
callback or array of callbacks.

2)  Functions (e.g. jQuery has some) that deep-clone object graphs and 
wants to turn arrays into [] in the clone while turning other objects 
into {}.  A special case of this is implementations of structured 
cloning, or indeed JSON.stringify.

3)  Sanity checking of input parameters to functions.  One could argue 
that this is misguided, or that it saves debugging time; I've seen 
people make both arguments.


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