Get element's custom css properties (-mystyle) using JavaScript

Question

In an application where certain elements have custom CSS properties, is there any way to retrieve such a value via JavaScript?

e.g.

Answer 1

Non-recognised CSS properties will be ignored when put within the style attribute, or in the style.cssText property.

If you want to define a property at a specific element, I recommend data-attributes:
HTML:

JavaScript:

//jQuery's method to retrieve value:
$("#myDiv").data("custom-property");
//jQuery, without parsing:
$("#myDiv").attr("data-custom-property");

// Modern browsers, native JS:
document.getElementById("myDiv").dataset["custom-property"];
// Older browsers, native JS:
document.getElementById("myDiv").getAttribute("data-custom-property");