Array#lastIndexOf – fromIndex evaluation

Brendan Eich brendan at
Sat Nov 3 14:22:15 PDT 2012

Thanks for raising this -- please do file a bug as Rick suggested.


Asen Bozhilov wrote:
> According to the spec if fromIndex is NaN or undefined the search will 
> start from 0. Step 5 of Array.prototype.lastIndexOf performs 
> ToInteger(fromIndex).
> This is in contradiction with String.prototype.lastIndexOf, where even 
> if I pass a NaN or undefined for position value, the search will start 
> again from the end of the string.
> I am wondering what is the intention of that decision, because it 
> seems like bug in specification.
> Thank you.
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