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Javascript variables and DOM Selectors

I have a question about DOM selectors.

Is there a performance difference between;

This code:

if (document.getElementById("post-dropdown-menu-" + postID) && document.getElementById("post-dropdown-menu-" + postID).style.display != "none") {
            document.getElementById("post-dropdown-menu-" + postID).fadeOut(200);
            return false;
}

And this code:

var neededElement = document.getElementById("post-dropdown-menu-" + postID);

if (neededElement && neededElement.style.display != "none") {
            neededElement.fadeOut(200);
            return false;
}

I really want to know if browser or javascript doing DOM Select proc. again if element already used in a function.

about 4 years ago · Juan Pablo Isaza

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Accepted Answer · 2022-07-05T14:35:34.522Z

Of course the second one is faster because you only use query selector once which mean less processing.

and here is a test score using JSBench.

Note that the effect will never be noticed except if you are using this inside a loop or so.

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Javascript variables and DOM Selectors

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Andres GPT