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What to store...

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  • Ruth Lang
    Hi, I have a question concerning Javascript and the DOM: For example I want to highlight an element when moving the mouse over it. Does it make more sense to
    Message 1 of 2 , May 8, 2009
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      Hi,

      I have a question concerning Javascript and the DOM:

      For example I want to highlight an element when moving the mouse over it.
      Does it make more sense to store the id of the element, or the element
      itself:

      My information so far are:
      - it takes time to make a query on the DOM (with getElementById), so I think
      it would make more sense to keep the element itself in storage
      - is there a difference on required space between storing the id (=string)
      and storing the element (=DOM object), or is there no difference at all?

      Thank you very much for your help.

      Ruth
    • Jeff Schiller
      I m not an expert in internal browser workings but since the browser already has to keep the DOM object in memory, it would make more sense to store a
      Message 2 of 2 , May 8, 2009
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        I'm not an expert in internal browser workings but since the browser already has to keep the DOM object in memory, it would make more sense to store a reference to the DOM object in your JS.

        I would suspect that the storage costs for a reference to a DOM object is the equivalent of a single C++ pointer (4 or 8 bytes depending on your architecture) while the storage costs for the ID string would be at least the size of a C++ pointer (4 or 8 bytes) and at most the length of the string.

        As you say, storing the DOM reference reduces query time.

        Regards,
        Jeff

        --- In svg-developers@yahoogroups.com, "Ruth Lang" <R.Lang@...> wrote:
        >
        > Hi,
        >
        > I have a question concerning Javascript and the DOM:
        >
        > For example I want to highlight an element when moving the mouse over it.
        > Does it make more sense to store the id of the element, or the element
        > itself:
        >
        > My information so far are:
        > - it takes time to make a query on the DOM (with getElementById), so I think
        > it would make more sense to keep the element itself in storage
        > - is there a difference on required space between storing the id (=string)
        > and storing the element (=DOM object), or is there no difference at all?
        >
        > Thank you very much for your help.
        >
        > Ruth
        >
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