Check if object is an event in JS

Question

I have a function that might either be called explicitly or when an event fires. If it's triggered by an event, I need to ignore a function parameter that might otherwise have a useful value.

Is there a reliable, cross-browser way I can check whether an object is an event?

We've been using this, but realized it doesn't work in IE7 since Event is undefined:

var view = {
    save: function (data) {
        if (data.constructor === Event.constructor) {
            // It's an event.
        }
    }
};

Jordan Kasper · Accepted Answer · 2013-01-13T05:03:53.530

2

I suppose the "poor man's" way would be to just check for the existence of a certain method that all Event objects have - regardless of how they are created:

if (!(typeof data.altKey == "undefined")) {
  // it's an Event
}

EDIT

Since preventDefault isn't accepted in some versions of IE I've changed the solution to use a different property, really any common property should work just fine.

edited Jan 13 '13 at 05:03

answered Jan 13 '13 at 04:48

Jordan Kasper

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`preventDefault` is undefined in early versions of IE – danronmoon Jan 13 '13 at 04:50
And if you're supporting those versions of IE then you are supporting unsupported software. IE 6+ supports `preventDefault` (and it isn't even supported by Microsoft any longer). Sorry, but that -1 is a bit harsh. – Jordan Kasper Jan 13 '13 at 04:53
IE9 is the earliest version to support `preventDefault`. – danronmoon Jan 13 '13 at 04:56
Fair enough, my bad, but the same idea would work with a different property. Will update. – Jordan Kasper Jan 13 '13 at 04:58
1

As long as OP doesn't define the same property in a non-event it should be OK. – danronmoon Jan 13 '13 at 05:03
+1 In light of recent edits this seems to be the only way. – danronmoon Jan 13 '13 at 05:50

Check if object is an event in JS

1 Answers1