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Asked: 2026-05-26T22:10:33+00:00

I am trying to figure out why Date.parse (javascript) returns NaN when applied to

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I am trying to figure out why Date.parse (javascript) returns NaN when applied to a seemingly valid ISO 8601 date string when IE9 is in Quirks Mode. It works fine in Standards mode.

//ReturnsNaN in Quirks Mode, 1270574382557 in Standards Mode
document.write(Date.parse("2010-04-06T17:19:42.557"));  

//Returns NaN in Quirks Mode, 1270512000000 in Standards Mode
document.write(Date.parse("2010-04-06"));

In contrast, the following works in both Quirks and Standards for me

//Returns 1270549182000 in both Quirks and Standards Modes  
document.write(Date.parse("2010/04/06T17:19:42"));

Is anybody else seeing this behavior? If so, any ideas on why Date.parse is returning NaN?

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1 Answer

  1. Editorial Team

    First of all you should understand that quirks mode is basically an IE5 compatibility mode.

    It is triggered by not having a valid declaration.
    The main effect is that it causes the browser to use the IE5 box-model, which means that all your paddings, margins and borders, and anything else which affects the size of a box will be incorrect.

    So your Date.parse doesn’t work because there were no such feature – “parse ISO 8601 date” at those dates.

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