Asked  7 Months ago    Answers:  5   Viewed   58 times

Is it possible to detect, using JavaScript, when the user changes the zoom in a page? I simply want to catch a "zoom" event and respond to it (similar to window.onresize event).




There's no way to actively detect if there's a zoom. I found a good entry here on how you can attempt to implement it.

I’ve found two ways of detecting the zoom level. One way to detect zoom level changes relies on the fact that percentage values are not zoomed. A percentage value is relative to the viewport width, and thus unaffected by page zoom. If you insert two elements, one with a position in percentages, and one with the same position in pixels, they’ll move apart when the page is zoomed. Find the ratio between the positions of both elements and you’ve got the zoom level. See test case.

You could also do it using the tools of the above post. The problem is you're more or less making educated guesses on whether or not the page has zoomed. This will work better in some browsers than other.

There's no way to tell if the page is zoomed if they load your page while zoomed.

Tuesday, June 1, 2021
answered 7 Months ago

With the 2nd solution, you have to manually call the previous functions, making it hard to remove specific listeners (which, to me, sounds like something you'd rather want than clearing all listeners), while on the first solution, you can only clear them all at the same time, unless you want to emulate the first functionality.

Personally, I always use the first solution, because it has the advantage of not having to worry about clearing possible other event listeners.

The mozilla wiki also lists the advantages that the first solution works on any DOM element, not just HTML elements, and that it allows finer grained control over the phase when the listener gets activated (capturing vs. bubbling) with the third argument.

Monday, June 14, 2021
answered 6 Months ago

cracked it! :)

Thanks to some help from Tom Kersten who helped me with testing. Turns out the code isnt the problem.

Be warned.. if your client uses any kind of anti-virus software which intercepts web requests, it may cause problems here. In this case, Sophos Endpoint Security, which provides enterprise grade anti-virus and firewall protection has a feature called web protection. Within this features is an option to scan downloads; it seems that the SSE connection is treated as a download and thus not released to the browser until the connection is closed and the stream received to scan. Disabling this option cures the problem. I have submitted a bug report but other anti-virus systems may do the same.

thanks for your suggestions and help everyone :)

Thursday, June 24, 2021
answered 6 Months ago

For this purpose you should override moveTo and moveByPx methods of OpenLayers.Map for eliminate movestart event triggering for any actions except zooming.

Tuesday, September 21, 2021
answered 3 Months ago

Based on your question there are two events you need to catch.

  • First there is the console close event which is explained here: "On Exit" for a Console Application
  • Second you want to catch control c which is explained here: How do I trap ctrl-c in a C# console app

If you put these two together with your example you get something like this:

static ConsoleEventDelegate handler;
private delegate bool ConsoleEventDelegate(int eventType);
[DllImport("kernel32.dll", SetLastError = true)]
private static extern bool SetConsoleCtrlHandler(ConsoleEventDelegate callback, bool add);

private static MyExternalProcess p1;

public static void Main()
    Console.CancelKeyPress += delegate

    handler = new ConsoleEventDelegate(ConsoleEventCallback);
    SetConsoleCtrlHandler(handler, true);

    p1 = new MyExternalProcess();

public static void killEveryoneOnExit()

static bool ConsoleEventCallback(int eventType)
    if (eventType == 2)
    return false;

For a working ctrl c (fun intended) paste example:

Monday, November 22, 2021
Ionică Bizău
answered 2 Weeks ago
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