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JavaScript

Posted by Jiten Mehta
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Jiten Mehta
Front End Web Development Techdegree Graduate 21,209 Points

Question regarding the fisher yates shuffle function in JavaScript

Hi guys, hope everyone has had a wonderful festive period.

I'm somewhat new to javaScript and im trying to really understand how functions work.

Ive been studying the fisher yates shuffle function and i think I now understand how it works. There is one thing i dont understand however.

My shuffle function is below.

const myArray = [1, 2, 3, 4, 5, 6, 7, 8, 9];

  const shuffle = (arr)=>{

  let newPos,
      temp,
      i;
  for (i = arr.length -1; i > 0; i--){
    newPos = Math.floor(Math.random() * (i +1));
    temp = arr[i];
    arr[i] = arr[newPos];
    arr[newPos] = temp;
  }
  return  arr;
}

const randomArray = shuffle(myArray);

console.log(randomArray);

The queston i have is regarding the newPos let variable.

When declaring it as arr[newPos] why do i have to use the parameter arr?

Why can't i just use

    arr[i] = newPos;
    newPos = temp;

Hope that makes sense.

Thanks, Jiten.

1 Answer

Steven Parker
Steven Parker
243,266 Points
Steven Parker
Steven Parker
243,266 Points

This code is swapping two array elements, "newPos" is not the contents of either one, but it's the index value of one of them. So "arr]newPos]" represents the element located at that index just like "arr[i]" represents the other one.