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PODo older versions of javascript evaluate ("-1" < 0) as false?
 

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  1. PODo older versions of javascript evaluate ("-1" < 0) as false?
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    <p>A bit of js on my brother's eCommerce site computes and stores transaction totals every time someone checks out. Periodically, a negative value is stored for tracker_total_amount. While he tries to work out why, he's decided to hard code an override which should address the ~0.1% of transactions with nonsensical values. It looks like this:</p> <pre><code>var tracker_total_amount = parseFloat(tracker.total_amount).toFixed(2); if(tracker_total_amount &lt; 0){ tracker_total_amount = 0; } </code></pre> <p>Negative values have continued to show up in the system.</p> <p>Original theory:</p> <p>I don't think he should be using .toFixed, because that's going to cast tracker_total_amount as a string - which, in my mind, would have stopped the if &lt; 0 condition working as expected. I was quite happy with this explanation until I tested it and the override worked. See here: <a href="http://jsfiddle.net/yXTrz/" rel="nofollow noreferrer">http://jsfiddle.net/yXTrz/</a></p> <p>New theory:</p> <p>Different users are running different versions of javascript. Some very small subset use an ancient version of javascript which (instead of helpfully converting the string to a float like mine is doing) continue to treat it as a string and always evaluate tracker_total_amount as being > 0, preventing the override from firing.</p> <p>Question:</p> <p>Did older version of javascript behave in this way? Could some users still be running those old versions? Best of all - is there a way I can simulate legacy versions of javascript to prove my theory?</p> <p>Edit: I should point out all the important stuff (payment etc) relies on a server side calculated value. The numbers here are just what's stored in Google Analytics afterwards, so - while it's possible to manipulate - the results wouldn't be too atrocious.</p>
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    1. COI highly doubt it. If negative values are continuing, you have issues elsewhere or a rounding issue. Also note that this is not NaN friendly, although if you get NaNs, something is very wrong.
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    2. COI read that the Yeti Browser does support testing of different Javascript implementations, not sure tho: http://www.yuiblog.com/blog/2010/08/25/introducing-yeti-the-yui-easy-testing-interface/
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    3. COHere are two more theories: 1. some user is bypassing your JS validaton - there are numerous ways to do that, intentional or not. 2. there is a number which `parseFloat` parses differently from the server (NaN < 0 evaluates to false).
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