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Editorial Team
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Asked: 2026-06-06T15:40:25+00:00

I’m writing a GreaseMonkey script that modifies an attribute of an element with a

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I’m writing a GreaseMonkey script that modifies an attribute of an element with a specific ID, but I’m having some problems accessing it due to a nontraditional HTML hierarchy. Here’s the relevant HTML:

<body>
...
    <iframe id="iframeID">
        <html>
        ...
            <body id="bodyID" attribute="value">
            ...
            </body>
        ...
        </html>
    </iframe>
...
</body>

Where attribute is the attribute that I’m attempting to modify.

At first, not realizing I was working with an iframe and a nested body tag, I tried this:

document.getElementById('bodyID').setAttribute("attribute","value")

While this worked fine in Firefox, Chrome tells me that I can’t set the attribute of null, suggesting that it cannot find any elements with the id bodyID. How can I modify this attribute in a cross-browser friendly fashion?

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1 Answer

  1. Editorial Team

    You first need to pull the document of the <iframe>:

    document.getElementById('iframeID').contentDocument
.getElementById('bodyID').setAttribute("attribute","value");

    Live DEMO

    BTW, if you want to get the <body> node, you don’t need to give id or something like that, simply:

    document.body

    In your case, it’s the document of the <iframe>:

    document.getElementById('iframeID').contentDocument.body.setAttribute("attribute","value");

    A lot simpler… Isn’t it?

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