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Editorial Team
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Asked: 2026-05-22T02:42:52+00:00

I found this code online for shuffling array elements, it works well, but I

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I found this code online for shuffling array elements, it works well, but I can’t understand the for loop here

shuffle = function(o)
{ 
for(var j, x, i = o.length; i; 
    j = parseInt(Math.random() * i), x = o[--i], o[i] = o[j], o[j] = x);
return o;
};

any help is appreciated, thank you !

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1 Answer

  1. Editorial Team

    This is basically a misuse of the flexibility of the for loop.

    The general syntax for a for loop is:

    for (<init>; <condition>; <increment>) {
  <body>
}

    which roughly can be expressed as following while loop:

    <init>;
while(<condition>) {
   <body>
   <increment>
}

    Since both <body> and <increment> are both executed as if they were in the body of the while, anything that can go into the body of a for loop, can also be put in the <increment> expression of the for loop. You just have to separate the statements with commas instead of semicolons.

    Thus your for loop is probably better expressed as following while loop:

    var j, x, i = o.length; 
while (i) { // same as while(i != 0)
   j = parseInt(Math.random() * i);
   x = o[--i];
   o[i] = o[j];
   o[j] = x;
}
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