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JS has too many statements! This proposal makes it easier to do all the flexible things you can do with statements while still producing a useful result and plugging that back into an expression context. Compound expressions with side-effects are possible with comma-expressions, but limited and awkward, and they can’t bind temporary variables. ES4 had multiple variations on let, but this took up v
We need to define when a call is in possible tail position for safety purposes, and proper tail position for liveness purposes. An implementation MAY implement a call in possible tail position as a proper tail call (PTC) and MUST implement a call in proper tail position as a PTC. (Loosely speaking, implementing a call as a PTC is also known as tail call optimization.) The old ES4 proposal for prop
Typed objects provide portable, memory-safe, efficient, and structured access to contiguously allocated data. Certain kinds of typed objects can also expose a binary representation of their backing store, making them conveniently serializable and deserializable. Some use cases:
This is a wiki for the ongoing specification work of Ecma TC39, the technical committee tasked with standardization of the ECMAScript programming language. Most of the wiki is world-readable, meaning that anyone can view the pages. Certain sections are restricted to members of the technical committee. The wiki is running on DokuWiki, a wiki program for editing documentation. It has several feature
This page is a revision of deferred_functions to explain how to express it as a library in terms of the concurrency strawman and the generators proposal, and as an enhancement to the Q API from the concurrency strawman. Async Functions Ecmascript programming environments typically are single threaded and pausing execution for long periods is undesirable. ES host environments use callbacks for oper
This proposal has progressed to the Draft ECMAScript 6 Specification, which is available for review here: specification_drafts. Any new issues relating to them should be filed as bugs at http://bugs.ecmascript.org // Empty arrow function returns undefined let empty = () => {}; // Single parameter case needs no parentheses around parameter list let identity = x => x; // No need for parentheses even
This page contains a historical record of working drafts of the ECMAScript Internationalization API specification prepared by the project editor. Errors in the current draft should be reported as bugs at bugs.ecmascript.org.
This proposal has progressed to the Draft ECMAScript 6 Specification, which is available for review here: specification_drafts. Any new issues relating to them should be filed as bugs at http://bugs.ecmascript.org Overview First-class coroutines, represented as objects encapsulating suspended execution contexts (i.e., function activations). Prior art: Python, Icon, Lua, Scheme, Smalltalk. The “inf
This proposal has progressed to the Draft ECMAScript 6 Specification, which is available for review here: specification_drafts. Any new issues relating to them should be filed as bugs at http://bugs.ecmascript.org. The content on this page is for historic record only and may no longer reflect the current state of the feature described within. This proposal is inspired by ideas from Bosworth et.al.
UI frameworks often want to provide an ability to databind objects in a datamodel to UI elements. A key component of databinding is to track changes to the object being bound. Today, JavaScript framework which provide databinding typically create objects wrapping the real data, or require objects being databound to be modified to buy in to databinding. The first case leads to increased working set
Guards are used as a convenient syntax for enforcing user-defined invariants. They can be used as types, but can also enforce arbitrary constraints. Use guards to annotate variable and parameter declarations, function return results, and property definitions. Each guard is asked to approve an incoming value, the specimen, to determine whether to let it pass, coerce it, or reject it. Examples of us
A trademark represents a generative nominal type. A trademark has two facets: A trademark’s brander allows one to brand objects or sets of objects with that trademark. Objects can be branded by a trademark when they’re created or at any later time, but a brand is irrevocable: Once an object is branded by a trademark tm, it is forever branded by trademark tm. A trademark’s guard allows one to test
All major browsers (if beta versions are included) now support accessing stack traces from scripts. However, no single browser agree on the details of how stack traces are accessible. function f() { try { doSomething(); } catch (err) { alert(err.stack) } } f(); Should alert something like: ReferenceError: doSomething is not defined at f (http://www.example.com/temp.html:5:5) at http://www.example.
This Proxy API replaces the earlier proxies API. A summary of the major differences between this API and the previous API can be found on the old strawman page. To construct a proxy that wraps a given target object: var proxy = Proxy(target, handler); Both target and handler must be proper Objects. It is not necessary to use new to create new proxy objects. The handler is an object that may implem
under the Harmony version, but the Result would remain “object” under the default version. Version details TBD. Some JS on the web carefully tests both typeof x === “object” && x === null or equivalent in order to distinguish null from an object reference. Other code is less careful. The ongoing burden on JS authors, maintainers, teachers, and learners is a small but (over time) significant cost.
ECMAScript already has excellent features for defining abstractions for kinds of things. The trinity of constructor functions, prototypes, and instances are more than adequate for solving the problems that classes solve in other languages. The intent of this strawman is not to change those semantics. Instead, it’s to provide a terse and declarative surface for those semantics so that programmer in
This proposal describes a module system for ECMAScript. It describes the semantics of the core module system. See the module loaders spec for the companion proposal to provide a dynamic, reflective API for loading modules. See the modules examples page for highlights of the module system. See the modules rationale page for a description of the design rationale. See the modules semantics page for a
EcmaScript is frequently used as a glue language for dealing with content specified in other languages : HTML, CSS, JSON, XML, etc. Libraries have implemented query languages and content generation schemes for most of these : CSS selectors, XPath, various templating schemes. These tend to suffer from interpretation overhead, or from injection vulnerabilities, or both. This scheme extends EcmaScrip
This page contains a historical record of working draft of the ES.next specification prepared by the project editor. Error in the current draft should be reported as bugs at bugs.ecmascript.org July 25, 2011 Draft doc pdf Mostly typo corrections (thanks for all the reports) and corrections to problems that have been reported against ES5.1. See closed 6th edition bugs at bugs.ecmascript.org.
Provide portable, memory-safe, efficient, and structured access to compact (i.e., contiguously allocated) binary data, as well as an interface for external binary I/O facilities such as XMLHttpRequest, HTML5 File API, and WebGL. Desiderata:
As a mutually exclusive alternative to arrow function syntax, inspired by the long es-discuss thread Allen's lambda syntax proposal and echoes and followups since, here is a proposal for Tennent Correspondence Principle, AKA “Principle of Abstraction” full-strength blocks as better functions, both syntactically and semantically. An essential part of this proposal is a paren-free call syntax, but o
The harmony namespace is intended to contain approved proposals for the ES-Harmony language. The following requirements, goals, and means help to inform and guide development of proposed extensions and improvements to ES5 for ES-Harmony. Straw-man proposals live in strawman until approved by TC39, at which point they move into the harmony namespace, linked from the proposals page. — Brendan Eich 2
For performance reasons, we want a complex number to be represented in a single block of memory, which we call a value proxy. This value proxy should include both the real and complex components, plus a pointer to data/methods etc that are common to all complex numbers. The alternative of having separate proxy and handler objects (plus closure state) for each complex seems too heavyweight. We want
See harmony for requirements, goals, and means informing and guiding the proposals under development for ES-Harmony. Lacking a formal language specification, the following list is not definitive, but it should reflect consensus achieved so far in TC39. Anything can be revisited for a good reason, of course. The following list will grow, but not without bound before the next ECMA-262 Edition is con
See also: the discussion thread on the es-discuss mailing list. A tech talk on harmony proxies is available here. To enable ES programmers to represent virtualized objects (proxies). In particular, to enable writing generic abstractions that can intercept property access on ES objects. Driving forces:
(new Function).name === “anonymous” wanted by the Web, according to this webkit bug (function(){}).name === ““ may be wanted too, we suspect – we aren’t sure, though, so this behavior of some browser-based implementations is not strong precedent function f(){} assert(f.name === “f”) is implemented by several browsers, with name not writable and not configurable
Allow for destructuring of array and object data using a syntax that mirrors the construction of array and object literals. The destructuring can appear in assignment statements but also in various initialization and binding forms. The object and array literal expressions provide convenient means of creating ad-hoc packages of data, returning them from functions, etc. A common idiom for multiple r
Array destructuring is implemented in the Opera browser starting with Opera 8
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