Set attribute without value

Perhaps try:

var body = document.getElementsByTagName('body')[0];
body.setAttribute("data-body","");

The attr() function is also a setter function. You can just pass it an empty string.

$('body').attr('data-body','');

An empty string will simply create the attribute with no value.

<body data-body>

Reference - http://api.jquery.com/attr/#attr-attributeName-value

attr( attributeName , value )

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