There are several ways of checking if an variable is an array or not. The best solution is the one you have chosen.
variable.constructor === Array
If you are having issues with finding out if an objects property is an array, you must first check if the property is there.
variable.prop && variable.prop.constructor === Array
Some other ways are:
variable instanceof Array
This method runs about ~~1/3 the speed~~ as the first example. Still pretty solid, looks cleaner, if you're all about pretty code and not so much on performance. Note that checking for numbers does not work as
variable instanceof Number always returns
instanceof now goes 2/3 the speed!
So yet another update
Object.prototype.toString.call(variable) === '[object Array]';
This guy is the slowest for trying to check for an Array. However, this is a one stop shop for any type you're looking for. However, since you're looking for an array, just use the fastest method above.
Also, I ran some test: http://jsperf.com/instanceof-array-vs-array-isarray/35 So have some fun and check it out.
Note: @EscapeNetscape has created another test as jsperf.com is down. http://jsben.ch/#/QgYAV I wanted to make sure the original link stay for whenever jsperf comes back online.