Semantics of "indexed" string access

Maciej Stachowiak mjs at
Tue Jun 24 18:21:21 PDT 2008

On Jun 24, 2008, at 5:46 PM, Allen Wirfs-Brock wrote:

> I’ve taken a crack at cleaning up Pratap’s initial specification for  
> supporting direct indexing of strings, eg “abc”[1] yields “b”
> Here are the semantics that seemed to make sense:
> s[n]
> 1)  If s has an own property whose name is the same as the value of  
> n, the value of that property is returned.

Since s is a string value, not an object, then it cannot have any own  
properties. The autogenerated wrapper for s does have some own  

> 2) else If the value of n is convertible to a number that is within  
> the bounds of the string value, return a string containing the  
> corresponding character
> 3) else if try to resolve n as the name of an inherited property
> 4) else return undefined.
> In other words, indexing into a string with a “valid” index returns  
> that appropriate character unless somebody has explicitly defined a  
> property named by that index on the object.

It is not possible to define a custom property on a string value. On a  
string object you could.

I would suggest it makes more sense to make index properties of a  
string act like index properties of an array, but read-only.


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