Casting with JSDoc

[Ross Goldberg]

I'd like to be able to perform the equivalent of a cast in JSDoc.

e.g., I have the following JSDoc / JS:

/**@type{!HTMLOptGroupElement}*/

var og = document.createElement('optgroup');

The compiler warns correctly warns:

JSC_TYPE_MISMATCH: initializing variable

found   : Element

required: HTMLOptGroupElement

How can I perform a "cast" into an HTMLOptGroupElement from the Element returned from document.createElement('optgroup')?

Logically, I'd want something like a @cast annotation, that could look like:

var og = /**@cast{!HTMLOptGroupElement}*/ document.createElement('optgroup');

Thanks.

[Tom Payne]

var og = /** @type {!HTMLOptGroupElement} */ (document.createElement('optgroup'));

Note brackets around expression being typecast.

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[Ross Goldberg]

Thanks.

[Tom Payne]

Following up on this, casting the result of document.createElement, goog.dom.createElement, canvas.getContext, and similar examples is so common that it would be wonderful if the Closure Compiler could automatically type the return value of these commonly-used functions, where it can reasonably do so.

i.e., it would be wonderful if

  document.createElement('optgroup')

magically returned a "HTMLOptGroupElement", but there is no expectation that

  document.createElement(someExpression)

would do any type refinement.

This could break existing code like:

  var element;

  element = document.createElement('optgroup');

  // do something with element as an HTMLOptGroupElement

  // ...

  element = document.createElement('div');

  // do something with element as an HTMLDivElement

but I hope that such code is rare, and a simple variable rename is all that is required in any case.

Regards,

Tom