javascript - How to use addClass() to prepend the class in the element's class list -

i hav div in html

    <button id="abc" class="btn btn-primary btn-block"></button> 

i need add class 'alert-danger' on mouseover. used following code

    $(document).on("mouseover","#abc",function()     {           $(this).addclass("alert-danger");     }); 

this works fine , appends class @ end of class list below

    <button id="abc" class="btn btn-primary btn-block alert-danger"></button> 

but problem 'btn' , 'alert-danger' classes have common css rules. 'btn' takes priority (as first in list) , disables rules of 'alert-danger'.so button should 'alert-danger' class first in classlist.

    <button id="abc" class="alert-danger btn btn-primary btn-block"></button> // requirement  

how modify addclass() in order prepend class instead of appending it.

an alternative requirement.

you can mark !important css property in alert-danger class, prioritize css effect per requirement.

check fiddle demo.