Unsafe Names for HTML Form Controls

API Design?

Form-as-a-collection Design Decision

Form-as-a-collection is problematic for implementors and should be a concern for developers (because bugs can occur when unsafe names are used).

The idea of creating properties on a form creates a conflict. In Opera, the same key may appear twice in a for in loop. Opera, For In Loop, Same Key Appears Twice.

The elements collection is a safe alternative. By deprecating the non-standard mystery "similar to a collection" behavior of a form, authors would be discouraged from using it.

Developers can still safely access the properties directly from the elements collection. There is no need to standardize this.


The HTML 5 draft has merged in much of the Web Forms 2.0 specification, which attempted to standardize some of the browser inconsistencies, strange behavior, and bugs.

toString Example

This example contains a FORM element with two form controls, one named "length", the other "toString". A click callback is added to the FORM's length property. The body of the function calls the alert function with the FORM.

(Click the submit button to see what happens.)



The callback tries to alert the FORM but throws an error when the alert function attempts to call the form's toString property, which was shadowed by a form control.

Callable Collections

Many browsers make HTMLCollection collection a callable object. When called, document.forms(x) returns a form element whose name, id, or index matches the supplied argument x.

Callable HTMLCollection Example

The DOM does not standardize collections to be callable. There isn't a good reason to call a collection. The property access operators provide a standard, cross-browser alternative. Callable collections are not implented in Mozilla. This feature does not appear to be considered for inclusion in HTML 5 or Web IDL.

Map-like NodeList Collections

Many browsers implement Map-like quality on NodeList. In these browsers, elements are accessible off the NodeList by their ID.

Map-like NodeList Example

This behavior is nonstandard and may be present, but should not be used. It is one innovation of Internet Explorer, copied in Safari, Opera, and perhaps elsewhere.

Implementation developers and specifications authors must be aware of the permanence of API Design. We should all be cognizant of the impact that an API has on the future.

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