JavaScript: what does Object(variable)?

Question

I ran into a boolean test variable === Object(variable) but couldn't find anything that describes it.

Is it testing that variable is the same as Object(variable) and does Object(variable) cast this variable into object? Or does it do something else?

If it matches it will loop for (var key in variable) and uses key and variable[key] as parameters for another function. If it fails it uses just that variable as is.

Denys Séguret · Accepted Answer · 2015-05-11 13:41:57Z

3

It checks that

the variable is defined
its value is an object
its value isn't null (be careful: typeof null is "object")

This is probably the simplest way to check these 3 conditions and it looks like a reasonable test to run before to loop on keys in a very polymorphic function.

Another one would have been typeof variable === "object" && variable.

From the MDN:

The Object constructor creates an object wrapper for the given value. If the value is null or undefined, it will create and return an empty object, otherwise, it will return an object of a Type that corresponds to the given value. If the value is an object already, it will return the value.

edited May 11, 2015 at 13:41

answered May 11, 2015 at 13:16

Denys Séguret

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1 Comment

user1271930 Over a year ago

Perfect! "If the value is an object already, it will return the value." I was on the wrong page in MDN: Object.protoype. So, close but not close enough :)

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