dataset is not worked in ie 9, pitfall

dataset.js

var myElement = document.getElementById('myElement'), // contains attribute data-my-custom-value
    myCustomValue;
 
if(myElement.dataset !== undefined) { // standard approach
    myCustomValue = myElement.dataset.myCustomValue;
} else {
    myCustomValue = myElement.getAttribute('data-my-custom-value'); // IE approach
    myElement.setAttribute('data-my-custom-value', 'new value') // set new value on the data attribute
}