Test for undefined function in Javascript

So Safari keeps yelling at me for one开发者_JS百科 specific error.

I'm trying to use Google Maps API and call map.getCenter();. However sometimes, this happens before the map has been fully loaded.

So instead in my function I test for an undefined call like this:

if (map.getCenter() != undefined)

But that still errors out because I guess it doesn't even like making the call just to test the if the result is undefined or not?

Can I get some help here?

Thanks!

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I actually prefer something along these lines.

if(typeof myfunc == 'function') { 
    myfunc(); 
}

Just because something isn't undefined doesn't make it a function.

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if (typeof map !== 'undefined' && map.getCenter) {
   // code for both map and map.getCenter exists
} else {
  // if they dont exist
}

This is the right way to check for existence of a function.. Calling the function to test its existence will result in an error.

UPDATE: Snippet updated.

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if (typeof map.getCenter !== 'undefined')

Won't throw an error.

So, better yet, if (typeof map.getCenter === 'function') map.getCenter();

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Technically you should be testing if map is undefined, not map.getCenter(). You can't call a function on an undefined reference.

However, Google's own tutorial suggests that you invoke your JavaScript that accesses the API in a body.onload handler, so that you do not attempt to reference anything until all of the remote .js files are loaded - are you doing this? This would solve the problem permanently, rather than failing cleanly when your JavaScript executes prior to loading the API.

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I have been in the habit recently of using the typeof operator to test for things and types. It returns the type as a string which I think avoids some response type confusion.

if( typeof map.getCenter != 'undefined') ...

I'm not sure if it's more correct, but I find good results with this process.

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You should be testing whether map is undefined. In your current check your are still trying to execute the function call.

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Assuming that map.getCenter() is always a function, it's sufficient to just use this check:

if (map.getCenter) {
      var x = map.getCenter();
}

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The worked solution for me is try and catch,

const stopPropagation = (e) => {
    try {
        e.stopPropagation();
    } catch (err) {
        console.log("error with stopPropagation: " + err.error);
    }
}

const triggerClick = (e) => {
    stopPropagation(e);
};