Extract number between brackets and increment

JavaScript

existingId = 'foo_0_bar_0';
newIdOnly = existingId.replace(/foo_0_bar_(\d+)/g, "$1");
alert(newIdOnly);

getAndIncrementLastNumber(existingId);

function getAndIncrementLastNumber(existingId){
    alert(existingId);
    newId = existingId.replace(/\d+$/g, function(number) {
    return parseInt(number) + 1;
});
alert("New ID ==> " + newId);
}