"Cancel run" option?

[tomeru]

Not sure how feasible this is, but:

Often times I find myself breaking something in a way that results in a very long or impossible query. However, once hitting 'run' there is nothing that can be done to cancel this operation except waiting for the browser to terminate the operation (sometimes resulting in lost work as well).

In such cases it would be useful to have some 'cancel' button which just stops the computation...?

[longouyang]

Currently infeasible, but this is totally do-able once we switch to WebWorkers - I'll close this and open #47