Classes should not override JSObject::toString(ExecState *)

• Component: WebCore JavaScript
• Status: RESOLVED FIXED

JSObject::toString(ExecState *) implements the (internal) ToString type conversion operator defined in ECMA-262 9.8. That definition applies to all objects, so classes deriving from JSObject should not -- and have no reason to -- override toString.

The correct way to customize the string representation of host objects is to implement in their prototype either a toString() method or the [[DefaultValue]]() internal method. (The native [[DefaultValue]] uses toString, but Firefox compatibility will probably require overriding [[DefaultValue]] as well).

Created attachment 10454 [details]
Test matrix for an HTML element

This table shows the value of several expressions that (should) invoke ToString, ToPrimitive, [[DefaultValue]], and possibly toString and valueOf.

The table shows that, assuming it follows the spec, Firefox overrides [[DefaultValue]] so that when it's called without a hint, it does not invoke valueOf.

Classes that currently override JSObject::toString() are DOMObject, DOMNode, JSHTMLElement, Window, FrameArray, Location, Selection and History.

Created attachment 13473 [details]
Unfinished patch

[Sam Weinig]

Created attachment 14815 [details]
updated patch

[Sam Weinig]

Comment on attachment 14815 [details]
updated patch

Geoff gave me the thumbs up on this baby!

[Sam Weinig]

Landed in r21927.