Drop event fire more than once

The drop event handler fire more than once, it keep increase the number of times it fires after every Drag&Drop operation!

I'm pretty sure that the code is right(everything is fine), but yet it is not working as expected. I'm working on a chrome extension.

$(".api").attr("ondrop", "drop(event)");

function drop(event) {
console.log("DROP");
event.preventDefault();
...
}