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Found 1 result

  1. var a = a || [ ];

    BACKGROUND: Earlier I posted a script from Matomo that serves as a counter for page hits and various other bits of information gleaned from a user's behavior on a webpage that bears the script. Although I now understand what the code does, I would like to understand its purpose. In particular, I would like to understand the probable reason for assigning to a variable another variable with the same name. The full code is given as: <!-- Matomo --> <script type="text/javascript"> var _paq = _paq || []; _paq.push(['trackPageView']); _paq.push(['enableLinkTracking']); (function() { var u="//{$PIWIK_URL}/"; _paq.push(['setTrackerUrl', u+'piwik.php']); _paq.push(['setSiteId', {$IDSITE}]); var d=document, g=d.createElement('script'), s=d.getElementsByTagName('script')[0]; g.type='text/javascript'; g.async=true; g.defer=true; g.src=u+'piwik.js'; s.parentNode.insertBefore(g,s); })(); </script> <!-- End Matomo Code --> The code of interest is var _paq = _paq || []; I find this piece of code problematic for three reasons: It assumes that this variable could already exist, but I have no idea where it could come from. It it does already exist what happens to the pre-existent with the same name. How does it know which value to choose? Is there a latent selection mechanism that tells the assignment operator to choose the second value when the first is undefined? Please advise. Roddy
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