Chrome: detect failed background script communication

[adam-p]

There seem to be two cases when requests from the content script to the background script can fail:

• When the extension upgrades in the background.
• On browser start, maybe with lots of tabs open, content scripts seem to be able to make requests before the background script is available.

I think that the failure can be detected by undefined being returned to a get-options request, say.

So...

• All requests need to have a return value, to detect the absence thereof.
• Do we retry? A finite number of times? Does that make sense for all requests?

[adam-p]

Mario Feaster (@ShamariFeaster) suggested a very good solution via email:

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My solution for problems like this is to use chrome.tabs.executeScript() when chrome.tabs.onTabActivated() and chrome.tabs.onTabUpdated() fires. But to protect against having a content script stranded without ports, as soon as a port is opened, I attach port.onDisconnected() and re-execute script when that event fires.

I also use a class I made called PortManager. It contains a map structure I call tabToPortMap. It looks like this < tabId:string, port_objects:array >.

I listen for chrome.runtime.onConnect() and when that fires, I add that port object to tabToPortMap that’s keyed on the tabId of the tab where the script was executed.

When I want to send a message to a tab, I get it’s available ports from tabToPortMap and then cycle through them, sending a message to each one. Since I have set this system up I’ve never had an instance of stranded content scripts.