Javascript map returning function

Question

I have an interesting problem with a map that is broken in Firefox. When I test if an empty map has the string "watch" it will return true and return the function watch(). I want that to return false since I haven't added the key "watch" to the map. A quick example

I normally create a basic map like

var myMap = {}
myMap["apple"] = 1;
myMap["pear"] = 2;

And to test if the map has the object I would write

if ("apple" in myMap) { ... }

And the problem is when I want to add the string "watch" to the map if the map doesn't all ready contain it. So when I check to see if the map contains "watch" it returns true.

if ("watch" in myMap) { ... }
// This also returns true.  and returns the function watch()

Any ideas on how to avoid this behaviour?

Thanks

Objects have built in properties, Object.watch being one of them, use a property name that isn't already in use, and it solves itself. — adeneo
– adeneo, Commented Jan 7, 2014 at 16:01

elclanrs · Accepted Answer · 2014-01-07 16:02:45Z

2

It's because an object literal inherits from the Object prototype. You can create an empty object, that inherits from nothing:

var myMap = Object.create(null);

Or check with hasOwnProperty:

if (myMap.hasOwnProperty('watch')) {
  ...
}

answered Jan 7, 2014 at 16:02

elclanrs

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1 Comment

Andrew Lichtenberg Over a year ago

Thanks. creating the empty object is what I needed to do.

Kevin Le - Khnle · Accepted Answer · 2014-01-07 16:02:45Z

2

You can try

var myMap = {};
myMap["apple"] = 1;
myMap["pear"]=2;

if (myMap.hasOwnProperty("apple")) {

}

if (myMap.hasOwnProperty("watch")) {

}

answered Jan 7, 2014 at 16:02

Kevin Le - Khnle

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