JavaScript for…in vs for

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The choice should be based on the which idiom is best understood.

An array is iterated using:

for (var i = 0; i < a.length; i++)
   //do stuff with a[i]

An object being used as an associative array is iterated using:

for (var key in o)
  //do stuff with o[key]

Unless you have earth shattering reasons, stick to the established pattern of usage.

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