Pure JavaScript contains a .map method too, it's on Array so you'd need to use it on the NodeList returned from querySelectorAll generically using .call:
var myProps = Array.prototype.map.call(document.querySelectorAll(".interp"),function (el) {
return el.id;
});
Alternatively, you can convert the NodeList to an array and use more compact syntax.
function query(selector){
return Array.prototype.slice.call(document.querySelectorAll(selector),0);
}
Which would let you do:
query(".interp").map(function(el){
return el.id;
}