I’m writing a web based application (large cargo aircraft weight and balance) in which the user enters pallet weights. When an individual pallet weight is entered, a number of checks have to be made to determine if that weight can be accepted. The checks are all relatively trivial in terms of compute cycles required; one is not. As I understand it, JavaScript is single-threaded, which I take to mean that if the user starts to enter a weight in another pallet position, he’s going to be locked out until the previous weight is fully processed.
I can’t afford to have the user waiting every time he enters a weight (which they don’t have to do at the moment as the app currently doesn’t make that last check properly). Currently I’m thinking of not doing the final compute-intensive step until all weights are entered and the user signifies so by clicking on a button. However, this will deprive the user of immediate feedback as to which weight initially triggered the problem, a problem in which multiple weights may contribute, and which is going to be hard to sort out if they have to wait until the last.
My Google searches on the topic have been somewhat useful, but I’m asking here for possible ideas for an up-to-date solution to the dilemma. Any suggestions are most welcome. The context of the problem can be observed by going to http://terryliittschwager.com/WB/JWB.php and selecting an aircraft.
If you want to do it client side, I’d recommend looking into WebWorkers. They run on a separate thread from the main (DOM) JS thread. Not supported in all browsers (of course), but is currently supported in Chrome, FF, Safari, and IE 10.
EDIT: The MDN for WebWorkers is a good place to start.