es6-work.md

Summary of high-level feature work for ES6

symbols

• new value tag
• sling throug hthe property sites
• audit tag examiners
• teach the jits
• ensure TI sanity with new jsids

tail calls

• strict mode only
• only function calls (including template strings), not member-expressions a.b or identifiers x that trigger getters
• calling through a proxy is the hard part
• coalescing AutoCompartments (to reduce to a bounded amount of memory the number of AutoCompartments we need to have for an unbounded number of tail-calls across compartment boundaries)

classes - syntactic sugar, frontend only

method shorthand

• frontend only (except super)

template strings

• frontend only, pretty much desugars to a function call
• String.raw

update let/const

• behavior in global scope ("lexical tier")

• for(let x in/of y) loop variable scoping (bug 449811); ditto in array comprehensions (bug 469402)

• temporal dead zone When you declare { alert(x); // TypeError let x = 2; } it's a TypeError to get x before it is assigned. { function f() {...} function g() {...x...} f(); let x = 2; } { let x = y, y; // TypeError even though we didn't try to do anything to y }

  • new opcode for "get let/const variable and check for undefined"
  • analysis (frontend? TI?) to determine, for any given access, whether it could be undefined.

• test262 for compliance

update destructuring

update Proxy

• audit minor spec changes
• audit getPrototypeOf sites for JS callbacks
• write new ScriptedProxyHandler hooks

modules

• frontend support
• module instance objects
• new import bindings, new opcodes, jit support
• debugger interactions
• linking
• Loader API

Realm API

• spec isn't done
• existing compartment infrastructure should make this pretty easy

WeakSet

• can self-host, or clone MapObject.cpp

super

• has a lot more new syntax than it "feels" like to users (just feels like a single new keyword, but many productions)
• interacts with classes, method shorthand, tail calls