Javascript function: Append string to object and return object value

Question

I need to get either the X position or the Y position of a mousedown event. So I tried passing a parameter to my getPosition function.

function getPosition(event, param) {
  // expected: var value = event.pageX;
  var value = event.param;
  return value;
}

$('#element').on('mousedown', function(e){
  var myValue = getPosition(e, 'pageX');
}

What am I missing here?

CodingIntrigue · Accepted Answer · 2013-09-27 07:39:32Z

2

You need to use bracket notation instead:

function getPosition(event, param) {
  // expected: var value = event.pageX;
  var value = event[param];
  return value;
}

If you use dot notation, the browser will look for a property called param on the event object, which doesn't exist. Using bracket notation, the browser will evaluate param and look for that on the object.

Here is a fiddle which demonstrates the code above.

edited Sep 27, 2013 at 7:39

answered Sep 27, 2013 at 7:33

CodingIntrigue

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2 Comments

Marc Owens Over a year ago

This works! Performance-wise, are there any drawbacks to this approach as opposed to using two separate functions getPositionX and getPositionY ?

CodingIntrigue Over a year ago

Performance-wise, bracket notation seems to be slightly slower. But you'd be doing well to even measure the difference between the two without calling it millions of times sequentially. jsperf.com/dot-vs-square-bracket/5

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