The HTMLTableElement.rules property represents which cell borders to render in the table.
HTMLTableElement.rules = rules; var rules = HTMLTableElement.rules;
rules is a string with one of the following values: nonegroupsrowscolsall// Turn on all the internal borders of a table
var t = document.getElementById("TableID");
t.rules = "all";
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https://developer.mozilla.org/en-US/docs/Web/API/HTMLTableElement/rules