The dataset read-only property of the MathMLElement interface provides read/write access to custom data attributes (data-*) on elements. It exposes a map of strings (DOMStringMap) with an entry for each data-* attribute.
The dataset property itself can be read, but not directly written. Instead, all writes must be to the individual properties within the dataset, which in turn represent the data attributes.
A DOMStringMap.
<div>
<math>
<msup id="equation" data-value="-1" data-equation="euler">
<mi>e</mi>
<mrow><mi>i</mi> <mi>π</mi></mrow>
</msup>
<mo>+</mo>
<mn>1</mn>
<mo>=</mo>
<mn>0</mn>
</math>
</div>const el = document.querySelector("#equation");
console.log(el.dataset.value); // "-1"
console.log(el.dataset.equation); // "euler"