Best way to check if variable is array?

[Mike Kypriotis]

I have read lots and lots of possible solutions all with its drawbacks, e.g. if it from a different frame or if it is a custom object including 'array' in its constructor, etc. but all more than 3 months old. The lattest mentioned Array.isArray([]) that comes with ECMAScript 5th Edition but do not work with IE7 and lower. Wanna know if there is a sure-proof solution for all?

P.S. For my particular application I take some arrays from JSON and want to check that they are arrays and then check teir length property to see if they have data inside

[Dormilich]

since JSON supports only the Object and Array objects, one of the old constructor checks is sufficient

[Mike Kypriotis]

found this page

http://perfectionkills.com/instanceof-considered-harmful-or-how-to-write-a-robust-isarray/

which concludes using

function isArray(o) {
  return Object.prototype.toString.call(o) === '[object Array]';
}

which is my best find so far, question is though that does not say which edition of ECMA-262 he took the definition of Object.prototyp e.toString (hoping its also working for 3rd edition cause I have tested the function for only the lattest browsers -5th ed)

[Dormilich]

toString() is a very, very basic method. that’s definitely not a recent addition

[Mike Kypriotis]

for a non framed enviroment (just taking some data from JSON) would u recommend this or instanceof? (have read that though the above is more complete -support multi-framed is slower and more complicated )

[Dormilich]

framed environment?

I’d use instanceof, the question is which version of IE supports that.

[Mike Kypriotis]

with "framed enviroment" meant working with multiple frames/windows and have to transfer an array from on to an other. From Javascript Bible found:
InstanceOf Compatibility: WinIE5+, MacIE-, NN6+, Moz+, Safari+, Opera+, Chrome+

[Dormilich]

I don’t think it has an influence on testing for an array.

[Mike Kypriotis]

not sure what u mean, tested this code

a = new Array(1,2,3);
a instanceof Array; //true
a instanceof Object; //also true but 
//I am interesting in testing for arrays

which is what i want but read that arrays are also of type object so tested

function userobject(str1){this.name=str1;}
a=new userobject("nikos");
alert(a instanceof Array);//false

which means that it distinguish object from array, so I am 100% sure of this working right?

P.S. On the other hand if want to test for both arrays and object determine which is which I will have to go with the prev solution right?

[Dormilich]

any non-primitive (undefined, null & the literals) inherits from Object because Object is the base of every object (including Array) in JavaScript.

[Mike Kypriotis]

So you mean that checking for undefined, null & literals with the InstanceOf Object will return true. But in case of checking with InstanceOf Array all is OK right?

[Dormilich]

those will return false, as they are not objects.

[Mike Kypriotis]

concluding for the job of checking some arrays in source code (not frames) and/or from JSON u would use instanceOf or Object.prototyp e.toString.call (o) === '[object Array]' ?

[Dormilich]

instanceof. toString() is easier to overwrite.