Info

This test is motivated by the use of duck typing in the current underscore.js implementation for _.isType() functions.

I believe we should not care about the cross frame edge case - take a look at the performance.

Preparation code

<script>
  var obj0 = [1, 2, 3],
      obj1 = {
    a: 5,
    b: 7
      },
      obj2 = [
    [
     []
    ]
      ],
      obj3 = 8,
      toString = Object.prototype.toString;
</script>

Test runner

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!! (obj0 && obj0.concat && obj0.unshift && !obj0.callee); !! (obj1 && obj1.concat && obj1.unshift && !obj1.callee); !! (obj2 && obj2.concat && obj2.unshift && !obj2.callee); !! (obj3 && obj3.concat && obj3.unshift && !obj3.callee);

obj0 instanceof Array;
obj1 instanceof Array;
obj2 instanceof Array;
obj3 instanceof Array;

toString.call(obj0) === '[object Array]';
toString.call(obj1) === '[object Array]';
toString.call(obj2) === '[object Array]';
toString.call(obj3) === '[object Array]';

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

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Revisions

You can edit these tests or add even more tests to this page by appending /edit to the URL. Here’s a list of current revisions for this page:

• Revision 2: published by Andi on 27th October 2010
• Revision 4: published on 8th October 2012
• Revision 5: published on 23rd October 2012

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