Today we continue to discuss jigsaw.Efficient, low effort mashup isolation by James Mickens and Matthew Finifter. Mashups are web applications that contain code from different principals.
Jigsaw lets mashups be isolated with its framework  and lets them selectively expose private state. We saw how Jigsaw improves the language and runtime for its purpose
We also saw that jigsaw has robust encapsulation tecniques for cross principal sharing. The execution context for the children are determined with the resource permissions and this is strictly dropping. All data is accessible by reference which is a performance gain.
Jigsaw introduces restrictions on the Javascript language. For example surrogate objects don't expose their prototype. The prototype of global builtin objects cannot be tampered. But Jigsaw supports many Javascript features and even improves them such as function objects, object literals, and pass by reference for objects shared across domains.
The compiler parses the Jigsaw code using ANTLR toolchain. The library implements the runtime security checks.
#coding exercise

We discussed Merlin QA in the previous message:
We discussed how to generate permutations
We calculate the benefit this way
Int getBenefit (List <Spell> spells)
{
Int benefit = 0;
Foreach (var spell in spells)
{
benefit += (new list <int> ( 0, spell [0], spell[0]+ spell [1]).max (); // the first two materials may suffice for determining relative cost between spells otherwise we can cumulate all materials for each spell.
The order in which we iterate is sufficient to find the cumulative across this order of spells.
}
Return benefits;
}