A JS related issues, I hope you help

A JS question, I hope you help
I have a layer that is called

He wants to use JS to replace class= "demo" With Id= "demo"

But var str= "" How to write here?

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First find the object, obj.id= ' demo '; Obj.classname= ";
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You already have an ID, don't you?
?
To modify into
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See clearly the question in reply! Come on

Document.body.innerHTML = Document.body.innerHTML.replace (/class=demo/i, ' Id=demo ');
This is a simple way of writing, to give you a clue
Complex and perfect please go to Web Development ――javascript Layout Solution
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So I was asking him what was the problem. haha
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Jquery
$ ('. Demo '). attr (' id ') = ' demo ';
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Explore

See clearly the question in reply! Come on

Document.body.innerHTML = Document.body.innerHTML.replace (/class=demo/i, ' Id=demo ');
This is a simple way of writing, to give you a clue
Complex and perfect please go to Web Development ――javascript Layout Solution

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