Can we change javascript onclick button to Salesforce lightning component attribute?

Hi Sushant,

You can get ID in the JS controller directly, no need to assign to another attribute,

Do like this:
In your component, assign the record Id to the button's Id

<aura:iteration items="{!v.newCases}" var="case">
<button type="button" onclick="{!c.showCaseDelete}" id={!case.Id}>Delete</button>
</aura:iteration>

In your JS controller, capture the ID as as source of event:

showCaseDelete: function(component, event, helper) {
var idx = event.target.id;
alert(idx); //here is your ID
});

Hope this helps you.

Thanks