Brendan Eich wrote:
Function.setTypeOf(V, U)
1. Let S = ToString(U)
2. Let T = V
3. If T is null then
3a. If S is not "null" and S is not "object", throw
4. Else
4a. If T is not a value object constructor, throw
4b. T = T.prototype
4c. If TypeofToExemplarMap.has(S), throw
5. Call TypeofToExemplarMap.set(S, T)
6. Call ExemplarToTypeofMap.set(T, S)
Correction, see new 4b below:
1. Let S = ToString(U)
2. Let T = V
3. If T is null then
3a. If S is not "null" and S is not "object", throw
4. Else
4a. If T is not a value object constructor, throw
4b. If T and Function are not same-realm, throw
4c. T = T.prototype
4d. If TypeofToExemplarMap.has(S), throw
5. Call TypeofToExemplarMap.set(S, T)
6. Call ExemplarToTypeofMap.set(T, S)
I did not add an exception when the current evaluation context's realm
is not the same as Function's -- that seems too restrictive, forbidding
script in the main window from fixing up typeof for same-origin code
that it loads into an iframe.
Again, comments welcome (cc'ing Allen since he is realm-master; ES1-5
left realm implicit and singular, contrary to reality in browsers).
/be
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