Bonfire: Diff Two Arrays - I had stuck here and finally figured out, pick up the right solution!
function diff(a1, a2) {
var a = {}, diff = [];
for(var i = 0; i < a1.length; i++) {
a[a1[ i ]] = a1[ i ];
}
for(var j=0; j < a2.length; j++) {
if(a[a2[ j ]]) {
delete a[a2[ j ]];
} else {
a[a2[ j ]] = a2[ j ];
}
}
return Object.keys(a).map(function(prop) {
return a[ prop ];
});
}
diff([1, 2, 3, 3], [1]);