javascript - Why on earth is jack showing up in the sequence of alert boxes? -

object.prototype.jack = {};  var = [1,2,3];  for(var number in a){     alert(number); }

could tell me why word "jack" jumped out of alert box?

thank much!

simple - arrays objects in javascript adding:

object.prototype.jack={};

you've added enumerable property 'jack' objects (and arrays).

once creating array "a" , looping through of properties

for(var number in a)

you sure 'jack' alert. avoid showing can use .hasownproperty() make sure alerted properties not inherited. or use regular

for(var i=0; < a.length; i++)

loop.

Sher