Is There a Spec That the Id of Elements Should Be Made Global Variable

Do DOM tree elements with IDs become global properties?

What is supposed to happen is that ‘named elements’ are added as apparent properties of the document object. This is a really bad idea, as it allows element names to clash with real properties of document.

IE made the situation worse by also adding named elements as properties of the window object. This is doubly bad in that now you have to avoid naming your elements after any member of either the document or the window object you (or any other library code in your project) might want to use.

It also means that these elements are visible as global-like variables. Luckily in this case any real global var or function declarations in your code shadow them, so you don't need to worry so much about naming here, but if you try to do an assignment to a global variable with a clashing name and you forget to declare it var, you'll get an error in IE as it tries to assign the value to the element itself.

It's generally considered bad practice to omit var, as well as to rely on named elements being visible on window or as globals. Stick to document.getElementById, which is more widely-supported and less ambiguous. You can write a trivial wrapper function with a shorter name if you don't like the typing. Either way, there's no point in using an id-to-element lookup cache, because browsers typically optimise the getElementById call to use a quick lookup anyway; all you get is problems when elements change id or are added/removed from the document.

Opera copied IE, then WebKit joined in, and now both the previously-unstandardised practice of putting named elements on document properties, and the previously-IE-only practice of putting them on window are being standardised by HTML5, whose approach is to document and standardise every terrible practice inflicted on us by browser authors, making them part of the web forever. So Firefox 4 will also support this.

What are ‘named elements’? Anything with an id, and anything with a name being used for ‘identifying’ purposes: that is, forms, images, anchors and a few others, but not other unrelated instances of a name attribute, like control-names in form input fields, parameter names in <param> or metadata type in <meta>. ‘Identifying’ names are the ones that should be avoided in favour of id.

In what standard is specified that elements with an id also get a global variable?

Its to do with the Document Object Model (DOM), which defines the logical structure of documents and the way a document is accessed and manipulated. it is not best practice and its better to use document.getElementById(); to avoid naming collisions etc.

Here is an example answer in response to this question previously.

id attribute on form element results in global variable

If you mean that it's available in browsers console than it's ok. It's just a way browser trying to ease the pain of writing document.getElementById('test'). At least it's the case with Chrome. If you open the Chrome console (for example on this page) and just type "sidebar" and hit enter, you'll see that it returns div with id "sidebar".

To answer directly to your question: it's completely normal to use an id on a form (or any other node) for that matter.

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