Introduction

Valija is approximately a subset of the ES3.1 "cautious" subset. But existing libraries are built for "consensus JavaScript", also known as "ES3 + Reality" (hereafter "ES3R"), as represented by what browsers currently do. On this page we try to enumerate all features of ES3R not available in Valija, so that we can more quickly spot problem areas in porting old JavaScript libraries to Valija.

Neither ES3.1 not Valija is settled yet, and actual browser behavior is determined only by ongoing experiment, so these lists are preliminary and fluid.

Details

In ES3R but not codified by any expected standards document

• Function.caller
• Function.arguments
• arguments.caller
• __proto__

In ES3 or ES3R but not in ES3.1

• crazy scoping -- ES3 specifies various gratuitous violations of lexical scoping that are crazy enough that most browsers often ignore the spec language and do something sensible instead.
• 'as if by the expression "new Array()"' -- if such language is interpreted literally, rebinding or shadowing the Array literal will cause, for example, array literal expressions to use the local binding to Array rather than the original built-in Array constructor.
• try/catch -- see Deviations document
• nested function expressions -- as with try/catch, ES3 specifies that the name is brought into scope by adding a new object to the scope chain. Therefore, according to the spec language, properties on Object.prototype will shadow lexical variables of those same name within the body of the nested function.
• Shared mutable RegExp literal

In ES3.1, but not in the ES3.1 cautious subset

• with
• this-promotion -- when a function mentioning "this" is called as a function, or reflectively with its "thisArg" bound to null, occurrences of "this" in the function become bound instead to the global object. In ES3.1 cautious, such use of "this" will cause an exception to be thrown. In Valija, the "this" will simply evaluate to null with no promotion.
• arguments.callee
• Joining of arguments array with parameter list
• delete <variable-name>

The continued adventures of block-nested declarations

• nested var declarations
• nested const declarations
• nested function declarations

In ES3R and ES3.1 cautious, but not in Valija

• eval()
• Function() constructor
• All identifiers ending in an underscore ("_")
• Distinction between a function's invoke behavior and its call or apply methods -- In Valija, we translate all calls into calls to the call or apply method of the invoked thing, which need not itself be a function.
• Function members inherited from Function.prototype --- call, bind, apply, and length are normally inherited from Function.prototype. In Valija, they are on each disfunction instance.

In ES3.1 cautious but not yet in Valija

• Reflective attribute control -- ES3.1 adds reflective attribute control operations on the Object() constructor.
• Decimal -- ES3.1 adds a decimal floating point library as an arithmetic alternative to binary floating point.
• getters and setters